关于路堤填筑方式，以下哪些说法是正确的( )。

A．不同土质混合填筑时应分层，每种填料层累计总厚不宜小于0.5m

B．优良土应填在上层，强度较小的土应填在下层

C．河滩路堤填土，路堤与护道应分别填筑

D．透水性较小的土填筑于路堤下层，应做4%的双向横坡

E．优良土应填在下层，强度较小的土应填在上层

The clean-up operation at the bullet train crash site in east China’s Zhejiang province has been completed. Meantime, trains have resumed services on the railway ______ the accident occurred.

A．which

B．that

C．where

D．the place where