三相交流电每相相位差为（）。
A、90°
B、0°
C、60°
D、120°
参考答案：D
Bring it nearer _____ I may see it better. [ ]
A. although
B. even though
C. so that
D. since
种子类中药显微鉴别的标志性特征是（）.
