I have been ringing the doorbell ____ a while, but there is no answer.
- To
- In
- For
- None of these
Explanation
"For a while" indicates a duration of time (how long the action continued).
Example: "I have been ringing the doorbell for a while."
"For" + time period = Duration (e.g., for hours, for days).
"Since" + specific time = Start point (e.g., since morning).
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