独立性地物符号除简要说明中规定按真方向表示外，其他的均垂直于南图廓描绘。( )
参考答案：对
函数f（x）=sin22x-cos22x的最小正周期是______．
Tom along with his classmates ______ for the coming exam.
[ ]
A. are preparing
B. are preparing themselves
C. is preparing him
D. is preparing himself
