The two sides adopted a Joint Action Plan in 2005 towards strengthening dialogue and consultation mechanisms in the political and economic spheres, _____________ trade and investment, and bringing peoples and cultures together.
We can understand that here, trade and investment is to be strengthened. Hence, option 4 is correct. The two sides adopted a Joint Action Plan in 2005 towards strengthening dialogue and consultation mechanisms in the political and economic spheres, enhancing trade and investment, and bringing peoples and cultures together.