The rate of metabolism of (a) / a body is comparatively lowest when (b...
Error: The error is in part (b) of the sentence. It should be "the body is at rest and" instead of "a body is comparatively lowest when".
Explanation: The sentence is discussing the rate of metabolism in a body at rest. The correct usage would be to use "the" instead of "a" before "body" as the sentence is referring to a specific body. The correct sentence would be "The rate of metabolism of the body is comparatively lowest when it is at rest and is thus optimum for examination."
The rate of metabolism of (a) / a body is comparatively lowest when (b...
IT SHOULD BE 'THE" INSTEAD OF 'A' BECAUSE IT ADDS DEFINITENESS AND MEANING TO THE SENTENCE.