What rule is being violated in the sentence?

In 1968, the Democratic Convention was held in Chicago, and the Republicans held their convention in Miami.]]> Using words and phrases in the answer bank, rewrite the entire sentence using active verbs. Then submit it and say the sentence.

In 1968, the Democratic Convention was held in Chicago, and the Republicans held their convention in Miami.]]> Using words and phrases in the answer bank, rewrite the entire sentence using passive verbs. Then submit it and say the sentence.

In 1968, the Democratic Convention was held in Chicago, and the Republicans held their convention in Miami.]]>