What day is considered to be the first day of a female's reproductive cycle?
When hormone levels are low and the uterus lining is shed.
When hormone levels are high and the uterus lining is shed.
When hormone levels are low and the ovary releases an egg.
When hormone levels are high and the ovary releases an egg.

When hormone levels are low and the uterus lining is shed.

Explanation:

The first day of menstruation - the day whenthe uterus lining starts to be shed. This is induced by a low level or hormones (this is also why some women feel down during this time)

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 your answer would be c.. : )