孟德尔一对相对性状的杂交实验中,实现3 :1的分离比必须同时满足的条件是( ) ①观察的子代样本数目足够多 ②F1形成的两种配子数目相等且生活力相同 ③雌、雄配子结合的机会相等 ④F2不同基因型的个体存活率相等 ⑤等位基因间的显隐性关系是完全的 ⑥F1体细胞中各基因表达的机会相等
On the way to Mount Heng,the scenery was so beautiful that all of us lost in it.( )
A.myselfB.themselvesC.ourselves
The last bus has left.What should we do?
Let's take a taxi.We have no other now.( )
A.choiceB.reasonC.habit
I haven't been back to my hometown for years.
______________!Your parents must miss you very much.( )
A.Of courseB.No problem
C.What a shame
Which invention do you like best?
QQ.It is an invention ____________ can help us communicate with others online freely.( )
A.whatB.thatC.who
The workers will complete the new bridge in ____________.( )
A.two and a half months
B.two months and half
C.two and a half month