Which of these synonyms best replaces the underlined word in the following sentence?

I love to see a child playing outdoors with child-like energy.

A. Young

B. Immature

C. Youthful

D. Undeveloped

The answer is C. Youthful

C. Youthful

"Child-like" as a word can best be replaced by the adjective youthful. It is the correct part of speech to fit into the rest of the sentence, and it means basically the same thing. Acting like a child is acting as one did in youth, so youthful and child-like are very close synonyms.