2. Because the measuring distance of the meter ruler is 1m and the measuring distance of the triangle ruler is less than or equal to 1m, only the measuring distance of the tape measure can reach several meters or even dozens of meters. The length of swimming pool is generally more than 50 meters, so it is obviously inappropriate to use meter ruler and triangle ruler, so it must be measured with tape measure.

To sum up, A is the correct choice for the third question.