My neighbour has a good gardener. The height of the tree in his garden is almost ______ the one in mine. [ ]

A. twice than

B. twice of

C. twice that of

D. twice

影响电除尘器工作的主要原因有以下几种分别是电极形式、（）、气流分布、供电电压、粉尘比电阻和粉尘浓度等。