命题p:直线l与抛物线C有且仅有一个公共点;命题q:直线l与抛物线C相切.则p是q的( )
A:充分不必要条件
B:必要不充分条件
C:充要条件
D:既不充分也不必要
如图所示,把玻璃管的裂口放在火焰上烧熔,它的尖端就变钝了,产生这一现象的原因是( )
给下面句子排序。(用数字表示)
①It's a knife.
②What's this in English?
③Excuse me, Wang Bing.
④Thank you.
____
________my bike was broken, ________ I went to school by bus yesterday.
如图所示,用食指顶起一把金属勺子保持水平平衡状态,OA段和OB段的重分别为G1和G2.则下列判断正确的是( )