Choose the correct meaning of idiom/phrase-
To be on cloud nine.
a. To die
b. To win a prize
c. To be very happy
d. To be unsure

Hint: A group of words established by usage as having a meaning not deducible from those of the individual words is known as an idiom.

Complete answer:
An idiom/phrase is a characteristic mode of expression in music or art. Here, we are asked to identify the meaning of the given idiom, “To be on cloud nine”. This phrase means, “to be extremely happy and excited.”

Let us examine all the given options to find out the correct answer :
> Option ‘a' is To die. This option cannot be the correct answer as this means, to not be living anymore, to end one's life. This does not match with the meaning of the given idiom.
> Option ‘b’ is To win a prize. This means to achieve something and get a prize. This also cannot be the correct answer as this doesn’t exactly convey what the given idiom is trying to convey.
> Option ‘c’ is To be very happy. This is the correct answer. It has the same meaning as the given idiom/phrase.
> Option ‘d’ is To be unsure. This phrase doesn’t have any relation with the given idiom/phrase.

Hence, the correct answer is option ‘c’, to be very happy.

Note: All the other options have different meanings, different context and are expressing different emotions. You need to figure out the correct answer in the correct context in such questions.