Manhatten SC 5th, chapter 13, verbs & Modifer, Helping Verbs小节中有这么一段话:
in the rare cases in which the tense do not need to match, the exact verb forming missing after the helping verb should be present elsewhere in the sentence.
Wrong: Our cars were designed to inspire envy, and they ARE.
Right: Our cars were designed to inspire envy, and they DO.
not agree啊,这里designed是被动语态的形式吧,整个谓语应该是were designed,即使要补出helping verb也是补be,而不是do
个人认为,楼主的例子,这里的do,是对inspire的
Our cars were designed to inspire envy, and they DO(inspire)
还是要看意思的吧,到底哪个更加和逻辑~