办理林权抵押贷款要严格把握抵押范围，下列哪些林权不得抵押（）。

A.生态公益林

B.权属不清或存在争议的森林、林木和林地使用权

C.自留山种植的林木

D.国防林

All the soldiers were placed exactly    the local government wanted them for the control of the comeback of the flood.

A．while

B．when

C．where

D．Though