The duck is ____ the lake.
A:in
B:on
C:at
观察这三幅图,按要求填空。
在上面看到 是____;在上面看到是 是____;在上面看到是 ____。
— I'd love to, but I think we shouldn't __________ our progress. We also have a long way to go.
导体在通常的条件下都有____。当导体材料在某一特定的温度下它的____为零,人们称之为____材料。