Final answer:
The simple sentence among the options is Option A, which has one subject and verb forming a complete thought without other clauses.
Step-by-step explanation:
The example of a simple sentence from the options provided is:
Option A. Animal testing is a cruel way to advance the progress of science.
A simple sentence is composed of a single independent clause with a subject and a predicate. Option A is the only one that fits this criterion, as it contains one subject ('Animal testing') and one verb ('is') to make a complete thought without any additional clauses.