---I have tried very hard to find a way out of the trouble, but failed.

---why not ask Frank for help? You see______________.

A．No pains, no gains

B．It’s better to think twice before doing something

C．Two heads are better than one

D．A friend in need is a friend indeed

按GB7588-2003《电梯制造与安装安全规范》规定，如果轿门的折叠门进入一个凹口内，则折叠门的任何外缘和凹口交叠的距离不应小于（）。

A、5mm

B、10mm

C、15mm