The retired teacher is said to have returned from the USA, where he ______ by some of his old students.

A．would be visited

B．visited

C．had been visited

D．have been visited

甲、乙两人玩猜数字游戏，先由甲心中任想一个数字，记为a，再由乙猜甲刚才所想数字，把乙所猜数字记为b，且a，b分别取数字0，1，2，3，若a，b满足|a-b|≤1，则称甲、乙两人“心有灵犀”，现任意找两人玩这个游戏，得出他们“心有灵犀”的概率为（    ）。