In the sentence "His hobby is writing poetry," the phrase "writing poetry" is a gerund phrase. A gerund phrase is verb+ ing which functions as a noun. In the sentence, the phrase "writing poetry" is a noun acting as a complement of the subject.
His hobby = writing poetry. This means "writing poetry" complements the subject "His hobby".
I thinks it's in a boardinghouse.
I've never gone to health for some reason, how's it like?
The children have been studying for the test
