A．ifB．onceC．whenD．whereas

【C5】A．untilB．onceC．afterD．since

A．unlessB．onceC．whileD．as

【C18】A．WhileB．OnceC．SinceD．Though

【C6】A．ifB．untilC．whenD．though

【C12】A．neverB．onceC．frequentlyD．scarcely

【C6】A．ThereforeB．At onceC．BecauseD．However