2. circle the letter of each sentence that is true about numbers expressed in
scientific notation.
a. a number expressed in scientific notation is written as the product of a
coefficient and a power of 10.
b. the power of 10 is called the exponent.
c. the coefficient is always a number greater than or equal to one and less
than ten.
d. for numbers less than one, the exponent is positive.

d.) circle motion requires a force to give it a centripetal acceleration.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)