when first _______to the market ,these products enjoyed great success.

问题描述:

when first _______to the market ,these products enjoyed great success.
A:introducing B:introduced
C:introduce D:being introduced

应该选B.
这是一句状语省略句.从句中的主语即是主句中的"these products".因为products与introduce之间是被动的关系,即"产品是被介绍/推荐"的.因此是用被动形式"introduced".
整句话的翻译是:当这些产品被首次推向市场时,就取得了很大成功.