Answer:
A. It is important to get exercise, but, be careful not do overdo it.
Explanation:
B and C have too many commas. After the word 'chicken' in B, there should be no comma. After the word 'cans' in C, there shouldn't be a comma there either. D ends with a comma, not a period, exclamation mark, or question mark, so the sentence was ended incorrectly.
This leaves us with A. At first you'd think the issue would be the comma after 'but', yet it makes sense grammatically. Putting a comma after but is the correct way to write a sentence, because 'but' is a transition word. When you use transition words in sentences, in most cases, you have to put a comma after the transition. This sentence is written correctly.
<em>A</em><em>.</em><em> </em>Is the right answer.
