旋盖后盖出现倾斜时，应调节旋盖头使其中心线与瓶口中心线重叠。
参考答案：对
If you are in any doubt as to _____ you should be doing these exercises, consult your doctor.
A．that
B．which
C．what
D．whether
海南石碌在主要矿产资源是______．
