What is the single most important element on Earth for life? (Science)

Eastern europe and parts of northern europe have which of the following climates?

Which of the layers of the earth has the following three characteristics? i. it is made of molten rock. ii. it has currents that are constantly moving. iii. earth’s plates float on top of its currents.

In the diagram below, ab and bc are tangent to o. what is the measure of