在下列哪种情况下，不论是自动或人工模式将会中断起动?（ ）

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

复合材料结构修理中的热修理是指

ELT工作频率为