Question

q: what is an invariable speed?
a. it is one that never changes.
b. it is one that is hard to measure.
c. it is one that changes frequently.
d. im not sure

Explanation:

The term "invariable" means something that does not vary or change. So, invariable speed refers to a speed that remains constant and does not change. Option b is incorrect as invariable speed's measurability isn't related to its definition. Option c is the opposite of what invariable means (changing frequently is variable speed). Option d is not a definition of invariable speed.

Answer:

a. It is one that never changes.