You can feel isolated at a party because Everyone else feels at home.

* Hướng dẫn giải

Isolated: cô đơn, biệt lập. => Đáp án là A. After all, if you are at a party you are not likely to try to strike up a conversation with a person who has a gloomy expression on his face and his lips turned down at the comers. So trying to look reasonably cheerful is a good starting point in combating loneliness, even if you are choking inside.