"People must take action now to protect coral reefs by reducing pollution and emissions of noxious gases." An opinion is a statement that expresses a judgement or viewpoint. All of the other statements express facts, they can be proven to be true.
Present participle.
example base verb. play
present participle - playing.
The correct answer is were.
Since English grammar has this thing called the sequence of tenses, which means that if the first verb in the sentence is in the past tense, all following verbs will have to be in the past tense as well.
So here, the first verb is <em>knew, </em>which is the past simple tense of the verb <em>to know, </em>which means that the following verb <em>to be </em>also has to be given in the past. The past simple form of the verb <em>to be </em>for plural is WERE.
