An expression whose definition is not usually predictable from the typical word meanings, such as kick the bucket. a. imagery b. puns c. idioms d. malapropism

The correct answer is C. idioms.
Idioms are phrases which consist of many words which don't seem to be connected in any way, however, they create a new meaning which cannot be simply predicted - you just have to learn idioms by heart.
Imagery is using descriptive vocabulary to create vivid images which could be easily imagined; puns are play on words; malapropism is wrong usage of a word.