I don‟t become a serious climber until the fifth grade,______ I went up to rescue a kite that was stuck in the branches of a treeA.when B.where C.which D.why

I don‟t become a serious climber until the fifth grade,______ I went up to rescue a kite that was stuck
in the branches of a tree
A.when B.where C.which D.why

A.When=at that time