作为子女，要孝敬父母；作为学生，要勤奋学习；作为朋友，要忠诚互助。这说明了（    ）

用三种不同的正多边形地砖铺满地面，若其中有正三角形，正八边形，则另一个为正____边形．

下列关于染色体和基因在亲子代间传递特点的叙述，错误的是（　　）

夹竹桃上下相邻的叶片互不遮挡，能使每片叶都尽可能多地接受阳光的照射。这种现象说明

    Last week, we asked some students about how to1 friends and if friends should 2the same or different. Here is what one of the students said.

    Jeff Green, a shy boy, said he is quieter and more serious than most kids. That's3he likes reading books and studies much 4 in class. He and his friend Yuan Li have one thing in 5: they are both quiet. Jeff thinks friends are like books — you don't need a lot of them, as long as they are good.