What is the IUPAC name of the compound CH3-CH2-CH2-COOH?

The compound contains a -COOH group, which is characteristic of a carboxylic acid.

Count all the carbon atoms in the main chain, including the carbon atom in the -COOH group.

There are four carbon atoms in the chain. The parent alkane with four carbon atoms is butane.

For carboxylic acids, the '-e' ending of the parent alkane is replaced with '-oic acid'. The carbon of the carboxyl group (-COOH) is always designated as carbon number 1, so its position does not need to be explicitly stated in the name.
Thus, butane becomes butanoic acid.

Comparing this with the given options:
A. propanoic acid (This would have 3 carbons)
B. butanol (This would be an alcohol, $CH_3-CH_2-CH_2-CH_2-OH$)
C. butanoic acid
D. Propanol (This would be an alcohol with 3 carbons)

The correct option is C.

The name of the compound is $\boxed{\text{C. butanoic acid}}$.