选B remain the best friends 他们仍然是最好的朋友.
(1)表示“继续保持或处于原来的状态”时,可用remain或stay,例如：
Three of them remained single.Shops should remain open till later in the evening.
The door stayed closed.But the police themselves prefer to stay unarmed.
(2)表示“需要设法才能保持或处于某种状态”时,应用keep,例如：
She knew she must keep calm.I wish those children would keep quiet.
Although they have many difficulties,they keep happy.