I learned the word worry contains two functions: one is as a transitive verb and the other is an intransitive verb.
However, in this two sentences, (from TOEFL)
People have a variety of factors in their lives that cause them to worry, such as school, jobs, and personal relationships.
Even during times when I was not actually studying, I found myself worrying about the tests and I was unable to completely relax.
I thought worry is a transitive verb, it must not go with preposition, such as about, whereas as an intransitive verb, it should involve preposition.
And I thought the worry in the first sentence is a transitive verb because it has object; a variety of factors in their lives. Thus, I agree with this sentence has no preposition.
However, in second sentence, I thought worry is a transitive verb since it has object: the test. Then why preposition about is there if worry in that sentence is a transitive?
Or does this word function as an intransitive verb? if so, why an object the test is there?