Exploratory testing would be a good test technique to use when under severe time pressure, because it is a type of experience-based technique that allows testers to design and execute tests based on their intuition, knowledge, and skills, without following a predefined test plan or test cases . Exploratory testing can be useful when testing time is very limited, as it can help to find important defects quickly and adapt to changing requirements or situations . The other options are not good test techniques to use when under severe time pressure. Option B is not a good option, because structure-based testing is a type of technique that requires analysing the code or design of the software under test to measure aspects such as code coverage, complexity, or coupling . Structure-based testing can be time-consuming and may not be feasible or effective when testing time is very limited . Option C is not a good option, because specification-based testing is a type of technique that requires analysing the requirements or specifications of the software under test to design test cases that verify the expected functionality or behaviour . Specification-based testing can also be time-consuming and may not be suitable or efficient when testing time is very limited . Option D is not a good option, because use case testing is a type of technique that requires analysing the use cases or scenarios of the software under test to design test cases that verify the end-to-end user interactions and outcomes . Use case testing can also be time-consuming and may not be relevant or effective when testing time is very limited .

The equivalence classes for the username string are based on the length of the string, not on the type of password or the error message. Therefore, option C is correct, as it divides the username string into two equivalence classes: shorter than 6 characters and equal to or longer than 6 characters. Option A is incorrect, as it does not consider the length of the username string. Option B is incorrect, as it does not specify the criteria for displaying or not displaying the error message. Option D is incorrect, as it confuses the username string with the password string.

Maintenance testing is a type of testing that is performed after a software product has been delivered and deployed to ensure that it still meets its requirements and functions correctly after changes have been made to it or to its environment. Changes can include corrective changes (fixing defects), adaptive changes (adapting to new platforms or environments), perfective changes (improving performance or usability), or preventive changes (avoiding potential problems). One of the appropriate reasons for maintenance testing is to verify that the software product works as expected after upgrading the operating system, which is an example of an adaptive change. Other reasons for maintenance testing can include verifying that the software product works as expected after fixing defects, adding new features, improving performance, or preventing future issues. You can find more information about maintenance testing inSoftware Testing Foundations: A Study Guide for the Certified Tester Exam, Chapter 12.

A consideration when deploying test execution tools is B. Recorded manual tests may become unstable in use. Test execution tools can record manual tests performed by a tester and replay them automatically on demand. However, recorded manual tests may become unstable or unreliable in use, due to various factors, such as changes in the system under test, changes in the test environment, changes in the user interface, timing issues, synchronization issues, etc. Therefore, recorded manual tests may require frequent maintenance or modification to keep them up to date and consistent with the system under test. A detailed explanation of recorded manual tests can be found inA Study Guide to the ISTQB Foundation Level 2018 Syllabus, pages 112-113

Statement coverage is not a black box technique, because it requires knowledge of the internal structure of the code. Black box techniques are based on the external behavior and specification of the software, without looking at the code.Equivalence partitioning, state transition testing, and boundary value analysis are all examples of black box techniques12