阅读短文，从方框中选择适当的单词填空。

Some people in Britain and America like to invite friends to dinner at home. But this is more common in America ____ in Britain. Don't worry if your English friends don't invite you home. It doesn’t mean that ____ don't like you.
When you are invited to an evening dinner, ask your friends what ____ you should arrive. It is a good idea to take a small present when you arrive, and it is ____ to say how much you like the house, the room, or the pictures in the room. But don't ask how much these things cost. In this way, ____  you and your friends will have a pleasant get-together.

下列选项中不属于酶的固定化技术是（ ）

关于对公式R=$\frac{U}{I}$的理解，下列说法中正确的是(   )