Large Shia Muslim populations are mainly found in

A. Kuwait, Bahrain, and Oman.

B. Iraq, Saudi Arabia, Bahrain, and Yemen.

C. Qatar, Yemen, and Kuwait.

D. Saudi Arabia, Bahrain, and Iraq.

The biggest Shia Muslim country is Iran (but it's not on the list). There is also a large minority in Iraq, Azerbaijan and Bahrain. Saudi Arabia has some small communities, but Yemen is divided almost in Half among the Shia and the Muslims - so the best answer is B! (but Kuwait also has a sizeable community and Quatar has about 5% of Shia Muslims)