Which of the following is suitable as a description of a bottom-up test compared to a top-down test?
a) A bottom-up test is more effective when applied to a newly developed system than to cases where a system is developed by revising an existing system.
b) In the final stage of the test, the discovery of problems in the interface between modules has a large impact.
c) A stub is required to take the place of a higher-level module that has not been developed.
d) In a bottom-up test, development starts at lower-level areas where there are many modules. Therefore, in the initial stage of development, it is difficult to do programming and testing in parallel.