Question

Sales of CDs have greatly increased since the early 1990s, when people _______ to enjoy? the advantages of this new technology.

A．begin	B．began?
C．have begun	D．had begun?

Answer 1

B?

此题考查since以及定语从句的时态照应。since加过去时间点，主句自然用完成时态。既然since跟的是过去的时间点，那么when指代的当然就是过去时间in the early 1990s，所以选过去式began。