However, you can use "monotonous" in various verb phrases depending on the tense you want to express. Here are some examples:
Present Tense:
* The lecture was monotonous. (Simple past tense)
* The music has been monotonous all day. (Present perfect tense)
* The job is becoming monotonous. (Present continuous tense)
* He always finds the routine monotonous. (Simple present tense)
Past Tense:
* The journey was monotonous. (Simple past tense)
* The work had been monotonous for weeks. (Past perfect tense)
* The weather was becoming monotonous. (Past continuous tense)
Future Tense:
* The meeting will be monotonous. (Simple future tense)
* The work will have been monotonous by the time he finishes. (Future perfect tense)
* The trip is going to be monotonous. (Future continuous tense)
Remember to choose the correct tense for the context of your sentence.