My grandfather has a painting by Picasso, it must be worth a lot

My grandfather has a painting by Picasso, it must be worth a lot of money.
【正确答案】：My grandfather has a painting by Picasso, which must be worth a lot of money.
【题目解析】：原句是两个单句，两个独立的单句不能用逗号连接。因此我们可以将其处理为定语从句。