题目

While we were running on the playground, Jack suddenly stopped ________ and lay on the ground, so we all stopped ________ what was wrong with him. A . to run; to see B . running; seeing C . running; to see D . to run; seeing 答案：C如图，AB是半圆O的直径，点P在AB的延长线上，PC切半圆O于点C，连接AC．若∠CPA=20°，求∠A的度数．