Fill in the blank with the most appropriate word. Thousands of traffic accidents _____ by careless drivers every day.

The correct answer is: are caused.

The sentence is in the present tense, so the verb “to cause” should also be in the present tense. The other options are not grammatically correct in this context.

• “Will cause” is in the future tense, which does not make sense in this context.
• “Caused” is the past tense, which does not make sense in this context.
• “Causing” is the present participle, which is not a complete verb and cannot be used as the main verb of a sentence.

Therefore, the correct answer is “are caused.”