对细胞免疫应答起负调节作用的细胞因子是()
A．IFN-γ
B．IL-10
C．IL-15
D．IL-12
E．TGF-β
参考答案：B,E
将点A（3，1）绕原点O顺时针旋转90。到点B，则点B的坐标是（ ）。
The children ______ a PE class on the playground when it suddenly began to rain. [ ]
A. have
B. are having
C. had
D. were having
