春天来了,树变绿了.

Spring has come, the tree changed green

Here comes the spring,with the leaf turns green.
And with what words to connect depend on your sentence.
The leaf is turning green,because the spring is coming.

涉及到时间状语从句,用when连接:

When spring comes,trees turn green.

spring comes and the trees are changing green.

Spring is coming, the trees become green.
是并列关系，可以不用AND来连接．

the spring comes, the trees are green