The plan was so shallow and impractical that no serious _______ was ever made to realize it.

A．recognition

B．comment

C．attempt

D．credit

蓄水池不得设于隧道正上方，水池基础应臵于坚实地基上；蓄水池顶部必须设防护棚，四周应设（），并有明显的安全警示标志，防止人员坠入。