What causes this periodic change in ocean level

Sea levels change for three main reasons: 1) As water warms and cools it expands and contracts; 2) The amount of water contained as ice on land surfaces changes over time; 3) The Earth's surface is dynamic and can move vertically.                                                                                    

Explanation:The first two reasons are directly caused by global temperature changes.

it has one origin of replication, but it proceeds in two directions - d)

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