The most important chemical catalyst on this planet is chlorophyll,______ carbon dioxide and water react to form carbohydrates.
A.whose presence
B.which is present
C.presenting
D.in the presence of which
为什么选D不选C呢?
______1810, water--powered textile manufacturing arrived in New Hampshire with the founding of a company in Manchester that manufactured cotton and wool.
A. Early
B.In the early
C.As early as
D.when early
答案是C,可是为什么不能选B呢? | 
