| | | | |
| 测定空气中O2的含量 | 验证浓 H2SO4 的腐蚀性 | 比较合金与纯金属的硬度 | 判断溶液的酸碱性 |
,(e为自然对数的底数).
的奇偶性,并用定义证明;
恒成立,求实数a的取值范围.
—Tuesday. I'll meet him at the interview tomorrow.

”的一个充分条件是( )
或
B .
且
C .
且
D .
或
Hello!My name is Anna. I am eleven years 1. I live in a house 2 the park. I have a friend. He 31.9 metres tall. He is 4 years old. I like to play football. But he5to play basketball. It's so easy for him!
,
,则
的非空子集的个数为( )