When using an echo sounder in deep water, it is NOT unusual to __________.

A
receive a strong return at about 200 fathoms (366 meters) during the day, and one nearer the surface at night
B
receive a first return near the surface during the day, and a strong return at about 200 fathoms (366 meters) at night
C
receive false echoes at a constant depth day and night
D
have to recalibrate every couple of days due to inaccurate readings
E