Isn't it necessary to ______ an apology

Isn't it necessary to ______ an apology It isn't necessary for us to know the causes of homeless什么意思 It isn't necessary for you to come tonday的同义句 Do you have to buy this hat?No,I________.It isn't necessary. 单项选择（ ）21.It isn’t ______ ring.It’s ________ eraser.A.an,an Don’t you think it necessary that he ______ to Miami but to 英语13.-Don’t you think it necessary that he ______ to Miami b It' isn't going to rain ,you an umbrella.A:needn't to take B isn't it an elephant?怎么回答 It's unfair of him to pay for everything,______?A.isn't it B -Isn’t it supposed to be very cold in Xi’an this time of yea make an apology to sb for