A question of "Helping Verb"

[FuM520]

In the book " 6th Sentence Correction" P202：

Wrong: Our cars were designed to inspire envy, and they ARE.

Right: Our cars were designed to inspire envy, and they DO (= do inspire envy)

In the " Wrong" version , what is the problem ? I am confused about the explanation in Manhattan SC book since it says " They Do inspire is acceptable, but they ARE is not grammatical"

However, my understanding is " Our cars were designed to inspire envy, and they ARE ( designed to inspire envy ) "

Whether the reason behind my question is that " This sentence wants to express an emphasis, thus, only " DO" could be used here ?

Hope reply

[Sage Pearce-Higgins]

Please try to post in the right forum: this forum is for questions from the GMAT Prep software.

You're right that the verb 'are' could refer back to 'designed', i.e. "Our cars were designed to inspire envy, and they ARE (designed to inspire envy)." But this sentence makes no sense. If I state that the cars were designed in a certain way, why do I need to repeat it? It would be like saying "I went to the shops, and I did."

The idea here is that we want to show that an attempted action was successful. For example, "He tried for a long time to pass the test, and in the end he did." Clearly, the 'did' is referring to 'pass', not to 'tried'.