What is the measurement 345.067 mg rounded to four significant digits?

A. 345.0 mg

B. 345.1 mg

C. 345.06 mg

D. 345.07 mg

count four from the first digit to the fourth one. When you see the fourth one, look at the digit after. if it is 5 + then the fourth digit increases by one. if 5 - then it stays the same. 6>5 so 0 becomes 1.

Therefore the answer is 345.1mg

significant digits start at the first nonzero number, so 345.067 to four digits is 345.1

The answer is A.