Question

4. She's an old friend – I ______ her ______ years.
(a) know – for
(b) 've known – since
(c) 've known – for
(d) knew – since

Answer 1

(c) be known ,for is the ans

Answer 2

She's an old friend – I 've known her  for years.

1. the phrase - 've known is a verb which is in present perfect tense.
2. the word -  for is a preposition which precedes the pronoun her.
3. verb is a doing word and it should always corresponds to the sentence tense as well as plural or singular form.
4. preposition establish the relation her and noun in the above sentence.

the correct option is (c) 've known – for.