Read each sentence to find out whether there is any grammatical error in it. The error, if any will be in one part of the sentence. The letter of that part is the answer. If there is no error, the answer is 'D'. (Ignore the errors of punctuation, if any). (solve as per the direction given)

The sentence reads: "A small baby breathes about 45 times per minute while a child of about six years breathes about 25 times per minute." Let's break it down to identify any grammatical error:

1. Option A - A small baby breathes about:
   • This part is grammatically correct. "A small baby breathes about" is a well-constructed phrase, and there is no issue with it.
2. Option B - 45 times per minute while:
   • This part is also correct. "45 times per minute" is properly structured, and the word "while" is used correctly to introduce the second clause of comparison.
3. Option C - a child of about six years breathes about 25 times per minute:
   • This part has a minor grammatical issue. The phrase "a child of about six years" is awkwardly structured. The more natural construction would be "a child of about six years old" or "a child of six years old." Therefore, "of about six years" is not the ideal phrasing.
4. Option D - No error:
   • There is a small error in Option C with the phrasing "a child of about six years," so this option is not correct.
5. Final Answer:
   • The error is in Option C. The correct answer is C.