Question

i have a pen. the pen is blue complex

Answer 1

Hey dear!
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You have asked to change the given sentence into a complex sentence. I have given two versions. So, see the answer below. 

Complex sentence- I have a pen which is blue in colour.

Or

I have a pen whose colour is blue.

Explanation. A comlex sentence contains principal clause and subordinate clauses or dependent clauses. In the above complex sentences - 'which is blue in colour' and whose colour is blue' are subordinate clauses.

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Answer 2

I have a pen which is blue I colour.