A theory has broad explanatory power but is difficult to test. What balance is necessary in scientific evaluation?

Correct answer: Testability is required along with explanatory power

The direct answer is B: testability is required along with explanatory power. A useful scientific theory should explain a wide range of observations, but it must also lead to claims that evidence can examine. The reasoning is: broad explanation gives the theory usefulness; a testable prediction allows observation or experiment; evidence can then support, modify, or reject the theory. Option A is wrong because broadness alone cannot show that an explanation is correct. Option B is correct because scientific evaluation needs both scope and the possibility of testing. Option C is wrong because difficulty does not make a theory true; a difficult test may simply require better methods or may reveal problems. Option D is wrong because scientific ideas are not accepted merely on assertion or authority; they need evidence and critical checking. Testability does not mean that every test is easy, only that the claim can in principle be compared with observations. Memory cue: a strong scientific idea should explain much and risk being checked.