什么是氢致开裂？
参考答案：
氢侵入钢中形成局部聚集、致使在钢材轧制方向发生台阶状开裂现象称为氢致开裂。
已知函数f（x）=ex-e-x（x∈R），
（1）判断函数f（x）的奇偶性与单调性；
（2）是否存在实数t，使得不等式f（x-t）+f（x2-t2）≥0对一切x都成立？若存在，求t，若不存在，说明理由．
—How do you find the health club?
—I . Everyone is saying its management is going from bad to worse
A．ought to join
B．should have joined
C．would rather not have joined
D．would like to have joined
