下列关于CFM56-5B发动机VBV说法正确的是：（ ）

Let us get ______ this old barn. It is of no use to us.

In some countries men usually have to _______ when they reach the age of 55.

John wrote to a pen friend in England _______ for several years.

These envelopes are so small that letters have to be ____several times before they can be put inside.

In old times, property was usually handed _____ to the oldest son at death of his father.

复合材料优点正确的是

雷达罩主要的材料是

下面哪个一般不会做为飞机复合材料的蜂窝夹芯材料

复合材料常见的损伤形式不包括

飞机上使用最多的复合材料纤维是哪一种