----_____has been designed to enable children and young people to act safely on roads?

----Programmes and resources in the theme “Road Safety”.

A．Why is it that

B．What is it that

C．What is that

D．Is it what

起重机主要结构件腐蚀深度达原厚度的（）时，则应予报废。

A.15％

B.10％

C.7％