monotonous

工厂装配线通常涉及单调的任务。

Factory assembly lines often involve ___monotonous tasks.

他单调的语调让整个讲座难以忍受。

His ___monotonous tone made the entire lecture unbearable.

他的声音如此单调，以至于让每个人都睡着了。

His voice was so ___monotonous that it put everyone to sleep.