Ahealthy 34 year old woman who is in first trimester of pregnancy and hasn't gained any weight yet should:
a. increase her calorie intake by 500-800 calories above her pre-pregnancy needs.
b. start taking a prenatal vitamin with more fat soluble vitamins.
c. immediately call her doctor to schedule an ultrasound and check for problems.
d. not be concerned at this time.

d. not be concerned at this time.

Explanation:

A healthy 34 year old woman who is in first trimester of pregnancy and hasn't gained any weight yet should not be concerned at this time. This is because, the baby isn't grown all the way yet and sometimes women won't even have a big stomach. Therefore, t is nothing to worry about.

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.