not... until, get everything ready, he, for the experiment, leave, the lab, Xiao Wang
A.
It was not until he got everything ready for the experiment that Xiao Wang left the lab.
B.
It was not until he got everything ready for the experiment which Xiao Wang left the lab.
C.
It was not until he got everything ready for the experiment when Xiao Wang left the lab.
D.
It was Xiao Wang who did not leave the lab until he got everything ready for the experiment.