基因的自由组合发生在(     )   

据报道，中共十七届中央委员会委员．候补委员和中央纪律检查委员会委员的预选，采用了差额选举办法，差额比例在百分之八以上。差额选举的优点表现在

某校从高一年级学生中随机抽取60名学生，将其期中考试的数学成绩（均为整数）分成六段：40，50），50，60），…，90，100后得到如下频率分布直方图．

在方框中填入一个恰当的词、或填入所给单词的适当形式，使短文通顺、正确、连贯。
    A lot of people wish to be slim, but at the same time they are____（worry）about their health. In fact, it is important for everyone to lose weight healthily. A strong body can keep you working in a high speed and make you more positive every day. However, how can you do it? Here's some good____（advice）.
    ●Drink plenty of water and eat____healthy diet. If you feel like____（eat）snacks, drink a glass of water first. If you are still hungry after 15____（minute）, then it's time for a light snack. Try to stay away from food with high calories, such as sweets and fast food.
    ●Do not eat____(much) than you can consume (消耗). People get fat because they can’t consume all the calories ____they get. So, knowing how many calories you really need is very important.
    ●Take enough exercise.  The  “333” is good   for you—exercise three____(time) a week, for at least 30 minutes at a time, and your pulse rate (脉搏率) should be more than 130 after____(exercise).
    Keep the three pieces of advice in mind and follow the advice. Then you'll____(sure) have a slim and strong body.

塑料梳子梳头发时，头发容易被梳子“粘”起，下列现象中“粘”的原因与其相同的是（   ）