We decided to give our teacher a surprise for her birthday yesterday. The classroom was cleaned and nothing...
(leave) on the floor. ​

Yesterday, we decided to give our teacher a surprise for her birthday. To make sure everything was perfect, we cleaned the classroom thoroughly. We made sure that there was no clutter on the floor.

In the given sentence, we need to choose the correct verb form to complete the sentence. The key is to understand the tense and subject-verb agreement.

Since the action took place in the past, we use the past tense. The subject "nothing" is considered as a singular noun, so we need to use the singular form of the verb.

The correct verb form to fill in the blank is "was left."

Therefore, the complete sentence is:

"The classroom was cleaned and nothing was left on the floor."

By using the past tense verb "was left," we are indicating that no items or objects remained on the floor after the cleaning process. This phrasing clearly communicates that the classroom was completely clean and ready for the surprise celebration.