①核糖体蛋白的mRNA ②胰岛素的mRNA ③抗体蛋白的mRNA ④血红蛋白的mRNA( )
A:①③
B:①④
C:②③
D:②④
写出下面各图形的面积.(每小格为1平方厘米)
It's a snowy day. Let's make a snowman. Let's make a big snowball for his ____, and a small snowball for his ____. Let's draw his ____. Let's put two sticks for his ____. Let's put a hat on him. I ____ he's wonderful!
小新同学按教材中的家庭小实验自制汽水,可是家里没有冰箱,为了使自制的汽水变得冰凉可口,他想到可以从集镇上购买一种商品来产生制冷效果,他应该买的是( )