人的一生中身体发育和智力发展的黄金时期是青春期，进入这一时期后，男孩出现____，女孩出现____。标志着人具有了生殖能力。

3.6＋1.7＝（   ）

     I like taking a long walk in the nature park. I do that    1  . It really makes a great    2   to the whole day! I usually walk up this nice long road. It's so quiet and pleasant   3   there are so many green trees.
    This morning, I walked on that road as usual.  4I was walking back down the road, on my way back    5 the car, I met a man. I saw him   6 on the grass by the roadside. He was breathing(呼吸) really    7 . I asked if he was OK. He said he was   8  tired to walk anymore. I thought he needed some  9  . So I began to look for some clean water.    10 , there weren't any places to get water in 11  a nature park. I walked back to my car    12  to see if there was some. Because I sometimes bring bottled water and leave    13in my car. Thankfully, I found some today.
    Instead of (代替) drinking it myself, I drove back to the man and gave him my bottle of water. Then I gave him a   14   back to his car. He was so thankful! I could tell he was very happy and surprised that someone was    15   to come back for him and give him some water. And also, I was very happy that I could share my water with others.

小红同学在镜子前用塑料梳子梳头，她发现头发会越梳越蓬松，这是因为摩擦后头发带了____电荷（选填“同种”或“异种”），这种使头发带电的物理过程称为____．

右图是由3个圆所构成的类别关系图，其中Ⅰ为大圆，Ⅱ和Ⅲ分别为大圆之内的小圆。
下列符合这种类别关系的是 (    )