The Best Evidence to Suggest That Sperm Counts in Men

The best evidence to suggest that sperm counts in men have been declining over time comes from studies in which researchers

A) collected sperm from men in various cities and compared them to each other.
B) tracked sperm counts in 1000 men every 2 years over the past 10 years.
C) compared sperm counts in men who wear boxers to men who wear briefs.
D) compiled data from many studies of sperm counts that had been published over the past 50 years.
E) used a much more sophisticated method of measuring sperm than in the past.