Tom's never been to Hong Kong, _______?
A:is he
B:isn't he
C:has he
D:hasn't he
戈尔巴乔夫改革与赫鲁晓夫当政时的政策相比( )
—Sorry. I ________ to set my alarm clock.
某植物花瓣的大小受一对等位基因A、a控制,基因型AA的植株表现为大花瓣,Aa的为小花瓣,aa的无花瓣.花瓣颜色受另一对等位基因R、r控制,基因型为RR和Rr的花瓣是红色,rr的为黄色,两对基因独立遗传.若基因型为AaRr的亲本自交,则下列有关判断错误的是( )
—Thank you, Mr Smith. I will and remember it.