Question

The most important thing in the world was silence. (change into complex)

Answer 1

Silence is important in the world

Answer 2

The given sentence " The most important thing in the World was silence"  is a simple sentence. It can be changed to a complex sentence by expanding a phrase or a part of the sentence.

This can be done as follows: The thing that is most important in the world was silence. In this complex sentence the part of the sentence "most important thing in the world" has been expanded to "the thing that is most important in the world is silence".