When first ＿ to the market,the computer software was not a success due to its complexity in ...When first ＿ to the market,the computer software was not a success due to its complexity in operation.A.introducing B.being introduced C.introduced D.to be introduced 为什么本题考查的是省略而不是非谓语动词?

选C. 省略了主句的主语.When (it's) first introduced to the market, the computer software was not a success due to its complexity in operation.

when (it was) first introduced ...省略主语和系动词，主句\分句的主语都是 the computer software电脑软件，“当电脑软件第一次被介绍到市场上时，由于它操作起来很复杂，所以并不成功。”
答案C 被介绍。

C 原句：when it was first introduced to the market, the computer software was not a success due to its complexity in operation.

选c 不是省略
When first introduced to the market, these products enjoyed great success.
当第一次投放市场，这些产品享有巨大的成功。