Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 15 to 18.Going to a party can be fun and enjoyable. If you are invited to a party, do call your host up early to inform him/ her of whether you are going. If you want to bring someone who has not been invited along with you, you should ask for permission first. Remember to dress appropriately for the party. You will stick out like a sore thumb if you are dressed formally whereas everyone else is in T-shirt and jeans. If you are not sure what to wear, do ask your host. During the party you may perhaps like to help your host by offering to serve drinks or wash the dishes. Your host would certainly appreciate these efforts. If you happen to be in a party you do not know anyone, do not try to monopolize the host's attention. This is inconsiderate since your host has many people to attend to and can not spend all his/ her time with you. Instead, learn to mingle with others at the party. You could try breaking the ice by introducing yourself to someone who is friendly-looking.Before you leave the party, remember to thank your host first. If you have the time, you could even offer to help your host clean up the place.If you are invited to a party, you should ________.