Swell is the rise and fall of the ocean’s surface due to（）.

A.the vertical rise or fall of the tide has stopped
B.slack water occurs
C.tidal current is at a maximum
D.the actual depth of the water equals the charted depth

A.when the moon is new or full
B.when the moon and sun have declination of the same name
C.only when the moon and sun are on the same sides of the earth
D.at the beginning of spring when the sun is over the equator

A.at the start of spring，when the Sun is nearly over the equator
B.only when the Sun and Moon are on the same side of the Earth and nearly in line
C.when the Sun and Moon are at approximately 90°to each other as seen from the Earth
D.when the Sun，Moon，and Earth are nearly in line，in any order