A．sinceB．atC．inD．after

Fifty million Americans are addicted（) nicotine.A toB atC inD on

A．toB．atC．inD．as

【C17】A．onB．atC．inD．within

【C19】A．ofB．atC．inD．for

【C10】A．forB．atC．inD．until

【C5】A．SinceB．After a whileC．AgainD．Before long