The correct answer is C.
This is correct because , in this sentence, the semicolon is joining two independen clauses with the conjunctive adverb "however."
A is not correct because semicolons cannot be placed after "and"
B is also incorrect because the semicolon is separating the subject "the plants" from its predicate "did not grow."
C is not correct either becase the semicolon is separating the verb "watered" from his direct object "the garden."
