Where should the comma be placed in following sentence?

The chameleon turning from tan to green, became invisible.

A) after turning

B) after became

C) after chameleon

D) There should not be a comma.

A) after turning

the answer was C!!!!1

Sorry about that, the website's automated answering system needs improvement...

I was very, very, aware that the automatic answering device did not do Physics; however it seems to also have an English problem.