题干
When he was a boy, he used to go there and watch _____.
A：to repair bicycle
B：bicycles to be repaired
C：bicycles being repaired
D：repairing bicycle
答案(点此获取答案解析）
C
（t为参数)点M、N在椭圆上，对应参数分别为 
， 
，则直线MN的斜率为