The answer is C, 我周六去游泳。
In the question, we need to select a proper response to the question above. The question translated into English should be "What will you do this weekend?".
A: "I sometimes go swimming, sometimes go training."
B: "I go training on every weekend"
C: "I go to swimming on Saturday."
D: "I go to swimming on Thursday."
Since the question is only about "this" specific weekend, so B is not correct. A is also not right because it doesn't answer the question. At last, D is not correct too because Thursday is not a weekend. So, the only correct answer is C.
