题干

经统计发现,XY型性别决定的生物,群体中的性别比例为1∶1,原因是(     )

A:雄配子数:雌配子数=1∶1

B:含X的配子数:含Y的配子数=1∶1

C:含X的精子数:含Y的精子数=1∶1

D:含X的卵细胞数:含Y的精子数=1∶1

上一题 下一题 0.0难度 选择题 更新时间:2015-04-14 07:17:44

答案(点此获取答案解析)

C

同类题4

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    Discovery Trips in the Blue Mountains.

    Bookings:

    Bookings for the following trips can be made by telephone (893﹣4847)or on the Internet at www.blue.mountain tour.Com

Black Bear Count

    There have been fires in Holly Woods in the last few years and the Office of National Parks is not sure how many black bears have been alive.The office has asked for volunteers to help count them.The whole trip will last three hours.Booking is essential (必须的).

Trip 1

Cost:Free When:Feb.8

Garland Valley

    Bring your binoculars and lunch for this walk in a beautiful area of the Blue Mountains.Garland Valley is close to the town of Garland but is part of the National Park.Many wild animals live in this  area,including many rare birds.This is a great walk for bird﹣lovers.The trip lasts four hours.

Trip 2

Cost:$15 When:Feb.8,15

Flashlight Adventure

    Put on your warm clothes,bring a flashlight and a pair of binoculars.Come for a night  walk along the Happy Valley and Secret Jungle in the National Park.Many of the animals you will see on the trip can only be seen at night.This walk lasts two and a half hours.

Trip 3

Cost:$12 When:Feb.8,15,22

Essential equipment

●Please bring enough water and food for all walks.

●Wear good walking shoes﹣﹣no high heels or sandals.

●Wear a hat for day walks.

●Dress warmly for night walks

●Children must be with an adult.

●Make  sure  your  flashlight  works  well  and  brings

extra batteries for night walks.

high heels×sandals×