题目

 Schools in the south tend to be better equipped, ______ those in the north are relatively poor. A. while   B. since    C. when   D. as 答案：A 如图，PA切⊙O于点A，PBC是经过点O的割线，若∠P＝30°，则的度数为 [　　] A．30° B．60° C．90° D．120°