My study in junior high school is coming to an end. It's time ____us_______.
A:for, graduate
B:to, to graduate
C:for, to graduate
D:to, graduating.
如图所示,三个线圈放在匀强磁场中,面积s1<s2<s3.穿过三个线圈的磁通量分别为Φ1、Φ2和Φ3,下列判断正确的是( )
单项式2x2y,﹣5x2y,﹣x2y的和是____
①调节粗准焦螺旋 ②调节细准焦螺旋 ③转动转换器 ④将观察目标移到视野中央.
— England.
下列各句中,标点符号使用正确的一句是( )