If two person had given your answer then there is a option of mark as brainliest. Click there in the option of mark as brainliest in which you like the answer most. If any one person has given answer then after some days you will a notification to mark his/her answer as brainliest. By this you can mark an answer as brainliest.
B is the answer I believe
the answer is - Americans are building on Dr.kings work
