2003.1------------40

liul781

40. Basalt, which composes most of the ocean floor, is a dark-grey rock rich in iron

A            B             C                   D

and magnesium than most surface rocks.

answer: D      rich---------richer       no problem

but how about C ?           floor--------floors

真老九

the ocean floor指的是海底，most ot the ocean floor海底的大部分，并不是most后面一定接复数，

rich>>>richer是因为后面有than，比较结构

liul781

thanks a lot!!