Explanation:

Correct Answer is (d).‘Complimentary’ means Free, which is of no relevance here, thus needs a replacement.
“Complementary “ is the correct word to be used here, which means corelated or corresponding.
Words like complementary, supplementary, contrary, corresponding etc. are always used with preposition ‘to’.
Correct sentence- We expect the addition of these two high quality portfolios to be highly complementary to our existing assets and to contribute to long-term leasing growth as India’s leading mobile operators accelerate their 4G network deployments.
Hence option D is correct.