设f（x）是定义在R上且周期为2的函数，在区间[−1，1）上，其中a∈R若，则f（5a）的值是（）.
参考答案：
The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.
A．to be based on
B．to base on
C．which to base on
D．on which to base
At the beginning of a speech, it is very important to grab the audience's attention and make them interested in ____ you have to say．
A．what
B．which
C．that
D．who
其中a∈R若
，则f（5a）的值是（）.
其中a∈R若，则f（5a）的值是（）.