Final answer:
The correct forms of the verb 'to be' for the given sentences are: are, is, are, are, is, is. The sentences 'Frogs are green,' 'It is a good film,' 'His feet are big,' 'Those are policemen,' 'This table is brown,' and 'The cat is in the box' demonstrate the correct usage of the verb 'is' or 'are' to match the subject of the sentence.
Step-by-step explanation:
To answer the student's questions regarding verb agreement in sentences:
- Frogs are green.
- It is a good film.
- His feet are big.
- Those are policemen.
- This table is brown.
- The cat is in the box.
In each sentence, you should select the correct form of the verb 'to be' based on the subject. If the subject is singular, use 'is'. If the subject is plural, use 'are'.