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______.