描述过去与现在的变化 — 英语选择题

根据提示选择正确的句子：过去我不会游泳，现在我会游泳。 A. I couldn't swim before, but I can swim now. B. I can't swim before, but I could swim now. C. I couldn't swim before, and I can't swim now. D. I can swim before, but I couldn't swim now.