Which line from the importance of being earnest is an example of a commentary on marriage?
“i don’t play accurately—any one can play accurately—but i play with wonderful expression.”
“the very essence of romance is uncertainty. if ever i get married, i’ll certainly try to forget the fact.”
“the bread and butter is for gwendolen. gwendolen is devoted to bread and butter.”
“it is a very ungentlemanly thing to read a private cigarette case.”

Well, the answer to this question should be very obvious - there is only one option that even remotely talks about marriage and that is the second choice - "The very essence of romance is uncertainty. If ever I get married, I'll certainly try to forget the fact."
The first example is about music, the third about Gwendolen loving bread and butter, and the final one about reading an inscription in somebody's cigarette case. So none of those choices even mentions marriage.

The very essence of romance is uncertainty. If ever I get married, I'll certainly try to forget the fact."

Explanation:

Why would a play such games with you.