Answer: B
how close their measurements are to each other
Explanation:
The students in a science class did not know the length of the board before taking turns to measure the length of a certain board.
The characteristic of their measurements that best indicates
their accuracy will be how close their measurements are to each other.
If the actual length is known before the carry out the measurements, there average value will be neccessarily to determine their accuracy.
Therefore, option B is the best option.