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21. Troposphere

22. Exosphere

23. Troposphere

24. Mesosphere

25. Crust

26. D

27. B

28. A

29. Sun

30. D

Explanation:

Troposphere is the layer of atmosphere that is present near to the earth surface whereas exosphere is the layer of atmosphere that is present farthest from the earth surface. Troposphere is the layer where weather of the earth is present. The mesosphere is the layer of the atmosphere that protects the Earth from meteoroids. Crust is the part of the earth on which we walk. oceanic crust and continental crust are the two types of crust. Mantle is the layer in which convection currents occurs. Convection currents refers to the rising of hot magma and sinking of cool magma. Sun is the source of energy and all energy comes to the earth from sun. Transitional boundary is not a types of plate boundaries.