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Overview of types of immune responses. Difference between innate and adaptive immunity. Differences between humoral adaptive immunity and cell-mediated adaptive immunity.

These three short online lessons discuss asteroids, comets and meteors.

There are some key words that you need to know for circles: radius, circumference, diameter, sector, segment, tangent, chord and arc. In this video you will discover what they all mean.

This video discusses the topic of circles.

This online resource discusses the distribution of earth's water.

These two short online tutorials discuss how the earth rotates and then the earth's revolutions.

In the first URL, the YouTube video explains why earth has spring, summer, autumn and winter seasons. The second URL summarizes the key takeaway points.

This online tutorial will explain the earth's shape and its hemispheres.

This video explains the equation of a circle.

This YouTube video explains how to calculate an irregular area on a map.