题干
—People in Southwest China have never experienced _____ natural disaster．
—Exactly．Let's do our bit to help them．
A：a more severe
B：the most severe
C：the more severe
D：a most severe
答案(点此获取答案解析）
A
，
，
，延长
，使
，连结
，求证:
.
是 三角形；
，且