基因是控制生物性状的____,基因是有____的____片段.
上海某中学的陶陶与豆豆是同班同学,他们有一段关于家乡的对话(如图)。请你阅读对话,回答下面小题:
— Come and join us, Ben!— I'm afraid I can't. I'm too busy now. If I ________ time, I would certainly go.