1. What is the root verb of 'seen'?

2. What is the base verb of 'seen'?
3. What is the bare infinitive of 'seen'?
4. What is the verb root of 'seen'?
5. What is the dictionary form of 'seen'?
6. What is the base from of the verb 'seen'?
-It's 'see.'
[Which expression in each question is ungrammatical?]

2 has the best phrasing. The rest don’t (unless there’s a typo in 6).

The answer should be phrased like this: It’s “to see.”

1. What is the root verb of 'seen'?

2. What is the base verb of 'seen'?
3. What is the bare infinitive of 'seen'?
4. What is the verb root of 'seen'?
5. What is the dictionary form of 'seen'?
6. What is the base form of the verb 'seen'?
-It's 'see.'
[Which expression in each question is ungrammatical?]

In the given set of questions, the only ungrammatical expression is in Question 6: "What is the base from of the verb 'seen'?" The correct expression should be "What is the base form of the verb 'seen'?"