2) there is an English grammar rule with COMPLEX OBJECT that say that "see" should be followed by either bare infinitive or 'ing':
see smb do smth; see smb doing smth
I came across a test that is a bit difficult to solve. However, I believe 'a' is the most appropriate, but it does not follow the grammar rule. why?
In the street, I saw Nataliya ...........by visitors.
a) surrounded b) surround c) surrounded
Because the rule that you cite is quite unconnected with the sentence at issue! When you say 'see somebody do/doing something', that person is the agent of the infinitive (i.e. the performer of the action). In your test question, there is no action performed by Nataliya; 'surrounded by...' is a simple participial postmodifier, meaning 'who was surrounded...'.