What is a front? What are warm fronts and cold fronts?

A cold weather front is defined as the changeover region where a cold air mass is replacing a warmer air mass. ... A warm weather front is defined as the changeover region where a warm air mass is replacing a cold air mass.

front- The boundary between two air masses that have different temperatures or humidity. In the mid-latitude areas of the Earth, where warm tropical air meets cooler polar air, the systems of fronts define the weather and often cause precipitation to form.

warm front-  A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient.

cold fronts-  A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone, at the leading edge of its cold air advection pattern—known as the cyclone's dry "conveyor belt" flow.

Explanation:

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answer; (d) melting of sea ice;