modal verbs - "It can contain" or "It can contains"?

What is the correct form?

1) It can contain

2) It can contains

Answer

As a native speaker I would say

1) it can contain

To use contains, the word "can" must be dropped, e.g.

2b) it contains

Only the modal verb (in this case, can) has to be in third person singular, the second part of the verb must be in bare infinitive form (because it is used after a modal).