一位农民种植的某块农田小麦产量总是比邻近地块的低。他怀疑该农田可能是缺少某种元素，为此将该块肥力均匀的农田分成面积相等的五小块，进行田间实验。除施肥不同外、其他田间处理措施相同。实验结果如下表。从表中可判断，该农田最可能缺少的元素是

A．K

B．N

C．P

D．S

Malaysia Airlines Flight 370 ___________ course and turned back toward Kuala Lumpur -- but there were no indications from the pilot that he was doing so.

A．must have changed

B．could have changed

C．might have changed

D．should have changed.