When first____ to the market, these products enjoyed great success.

A．being introduced   B．having introduced   C．introduced        D．introducing

When first _____ to the market, these products enjoyed great success.

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A．introducing　　B．introduced

C．introduce　　　D．being introduced

When first ________ to the market, these products enjoyed great success.

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When first ________ to the market, these products enjoyed great success.

[　　]

When first ________ to the market, these products enjoyed great success.

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