563.Over the past 3 decades the number of students leaving home each year to study abroad _______ at an annual rate of 3.9 percent,from 800,000 in 1975 to 3.5 million in 2008.
A.grew
B.grows
C.have grown
D.has grown
564.Years ago we didn't know this,but recent science _______ that women who drink more than two cups of coffee are more likely to have heart disease than those who don't.
A.showed
B.has shown
C.will show
D.is showing
563.答案是D;over/in/during the past 3 decades与完成时连用；the number作主语，谓语用单数，故选D。
564.答案是B;由recent science暗示，此题用现在完成时为妥。
