We haven't seen them ___Christmas.

We haven't seen them ___Christmas.
A until B while C since D to
我选择了A ,Why?

not ...until 引导时间状语从句,从句不能用将来时,主句是一般将来时,从句用现在时.
Don't get off the bus until it stops.(主句是祈使句从句用现在时）
He didn't go to bed until his mother came back.（主句是过去时,从句时态一致）
He won't call you until he finishes his work.(主句用一般将来时,从句用现在时）
since的用法：译作“自从…以来”
(1)接时间点：如 I have stayed in that country since 1995.要求：谓v.用现在完成时,而且须是延续性动词.
(2)接一段时间 + ago：如 They have lived in that house since two years ago.要求：谓v.用现在完成时,而且须是延续性动词.
(3)接时间状语从句：如 I have loved her since I met her last time./ Lily has stayed at home since she left school.要求：主句的谓v.用现在完成时,而且须是延续性动词；从句的谓v.用一般过去时,而且须是终止性动词.
(4)用于句型“It’s / It has been + 一段时间 + since + 时间状语从句”中,译作“自从…以来,已经…(时间)了”.如 It’s / has been three months since he moved to this city.要求：主句的谓v.用一般现在时或现在完成时；从句的谓v.用一般过去时,而且须是终止性动词.
(5)用于句型“一段时间 + has passed since + 时间状语从句”中,译作“自从…以来,…
(时间)已经过去了”.如上个例句还可写成：Three months has passed since he moved to this city.要求：主句的谓v.用现在完成时,而且动词必须是has passed；从句的谓v.用一般过去时,而且须是终止性动词.
(6)注：当since用于否定句时,主句的谓v.可以是终止性动词.如 He hasn’t seen the film since last month.
(7)相关词组：“从那时起”：ever since、since then、from then on.
注：ever since作为一个词组,放句尾可单独使用.如I have given up smoking ever since.另外,还可在since后接句子.since前加ever,只是加重语气而已.如 I have given up smoking ever since I caught a bad cough.
(8) since还可引导原因状语从句,译作“由于；因为”,相当于because.如 Since he was lazy,he didn’t finish his homework.
not until一般不与完成时态连用