1. Wang Xiang wrote the numbers according to certain rules: 1+2-34+5-67+8-9 ... When he finished writing the 50th number, he stopped. There are (34) positive numbers and (16) negative numbers in the number he wrote.

2. If one side of a square is reduced by 10% and the other side is increased by 1m, the obtained rectangle is equal to the original square area, so the original square area is (8 1) m2.

A bottle of pure alcohol is 200 grams, and 20 grams have been used. Fill it with water, which means the concentration of alcohol is (a)

90% B 10% C95% D45%