光从一种介质斜射人另一种介质中时，即光在不均匀的介质中传播时会发生______现象，由此可知，光只有在______介质中是沿直线传播的．

65. They are living in a        place and their houses are flooded almost once every year.

A．lie-low

B．low-lie

C．low-lain

D．low-lying