Sentence Correction (SC) | Re: The English physician Edward Jenner found that if experimental subject

The English physician Edward Jenner found that if experimental subjects were deliberately infected with cowpox,which caused only a mild illness, they are immune from smallpox.

A.which caused only a mild illness, they are immune from
B.causing only a mild illness, they become immune from
C.which causes only a mild illness, they are immune to
D.causing only a mild illness, they became immune from
E.which caused only a mild illness, they would become immune to