But drug-overdose rates, which were well below five per 100,000 people between 1950 and 1990, climbed above that rate by the turn of the century, and then spiked dramatically, reaching above 20 deaths per 100,000 in 2017.有两个问题一是从句中的well副词修饰介词below吗？另一个是above是介词吗？