Each statement contains a quantity. Rewrite each quantity using a power of 10.
A. There are about 37 trillion cells in an average human body.

B. The Milky Way contains about 300 billion stars.

C. A sharp knife is 23 millionths of a meter thick at its tip.

D. The wall of a certain cell in a plant is 4 nanometers thick. (A
nanometer is one billionth of a meter.)