训练有效咳嗽,气道内黏液必须有一定的________。
参考答案:厚度
This small seaside village is a perfect place for holidays so that visitors never leave it________. [ ]
A. felt disappointing
B. feeling disappointed
C. feeling disappointing
D. felt disappointed
我国发射的同步卫星,它相对于______是静止的,相对于太阳是______.