Which is an example of a simple sentence? a. because animal testing is so cruel, it should be stopped immediately. b. the practice of animal testing should be stopped and the labs dismantled. c. animal testing is cruel because animals suffer horrible deaths. d. animal testing is a cruel way to advance the progress of science?

The correct answer is D. Animal testing is a cruel way to advance the progress of science.
A simple sentence is one which has one predicate, or finite verb in it. In sentence D, the only predicate is IS, whereas to advance is infinitive, and thus cannot be considered a predicate. The other sentences have more than one predicate, and therefore are not simple sentences, but rather either complex or compound.

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