Aresearcher decides to test the scientific validity of the common phrase "an apple a day keeps the doctor away". what would be a valid hypothesis to investigate this specific question?

The correct answer is would be - Eating a single apple every day changes the frequency or number of visiting doctors.

Explanation:

A hypothesis is an explanation or an idea that is based on the observation with prior scientific knowledge which meant to be tested by the experiments and scientific methods.

In this phrase, one can get an idea about the effect of intake of an apple every day affects the numbers of the visits to the doctor it can be hypothesized by two hypothesis-

1) Eating an apple a day does not change the frequency of visiting the doctor. or.

2) Eating an apple on a daily basis decreases the number of visiting doctors.

Thus, the correct answer would be -  Eating a single apple every day changes the frequency or number of visiting doctors.

b. lithosphere, asthenosphere, mesosphere   is the answer most likely

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.