题目

Some kinds of birds in winter fly to the south to ________the cold in the north. A . get away from B . come up with C . break away from D . put up with 答案：A如图，∠XOY＝90°，OW平分∠XOY，PA⊥OX，PB⊥OY，PC⊥OW．若OA＋OB＋OC＝1，则OC＝（    ） （A）2－　 （B）－1　 （C）6－　 （D）－3