Sentence 8: Eventually his design became the norm for all roads everywhere.
If the beginning of sentence 8 was rewritten with "The norm for all roads", what should be the next words?

The sentence is written in the past tense; therefore, the verb needs to be in the past tense as well. The subject of the sentence is singular (design); therefore, the subject needs to not only be in the past tense, but in the singular as well. Thus, the appropriate option is: \u201Cwas his design.\u201D