46. Because of a _____ engagement, Lora couldn’t attend my birthday party last Saturday.
　　A. pioneer B. premature C. prior D. past
　　47. No new investments or acquisitions will be made without the _______ of Kolsen Reconds’ board of directors.
　　A. convenience B. adoption C. sanction D. event
　　48. ______ much is known about what occurs during sleep, the precise function of sleep and its different stages remains largely in the realm of assumption.
　　A. Because B. For C. Since D. While
　　49. The glass vessels should be handled most carefully since they are ______.
　　A. intricate B. fragile C. subtle D. crisp
　　50. Hill slopes are cleared of forests to make way for crops, but this only ______ the crisis.
　　A. accelerates B. prevails C. ascends D. precedes