How can a lock and key be used to describe an enzyme

The Lock and Key analogy is a theory that was first postulated by in 1894 by Emil Fischer. In this theory, the lock is the enzyme and the key is the substrate. The correct sized key (substrate) will fit in the key hole/active site of the enzyme (lock).

For example enzyme Amylase, amylase is the hereby the enzyme whereas starch forms the substrate. The molecule of starch will form the required shape and fit into the active site of the Amylase to undergo breakdown to form maltose

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.

i believe it would be c: tons.