Final answer:
Observation A is better evidence of a theory than observation B when it is supported by a larger amount of available evidence.
Step-by-step explanation:
Observation A is better evidence of a theory than observation B when it is supported by a larger amount of available evidence. In science, a theory is a general statement that explains a large number of observations. It is supported by significant evidence gathered through experiments and systematic observations. Observation A, which is supported by more evidence, provides stronger support for a theory than Observation B.