Answer
See the explanation below.
Work Step by Step
a) The height of Angel Falls is a measured quantity. This is not an exact number.
b) The number of planets in the solar system is a number count. This is an exact number.
c) The number of grams in a pound is not a unit definition. This is not an exact number.
d) The number of millimeters in a meter is a definition of prefix "milli" This is an exact number.
