What is the IUPAC name for the following structure: CH3CH(CH3)CH2CH2OH?

Number the carbon chain starting from the end closest to the -OH group to give the hydroxyl group the lowest possible number.

Let's write out the structure and number the carbons:

The longest continuous carbon chain containing the -OH group has 4 carbon atoms. This means the parent alkane is butane. Since it's an alcohol, the suffix changes to '-ol', making it butanol. The hydroxyl group is on carbon 1, so it is butan-1-ol.

There is a methyl group ($CH_3$) attached to carbon 3 of the main chain.

Combine the substituent name and its position with the parent alcohol name.
The name is 3-methylbutan-1-ol.

Now, let's compare this with the given options:
A. 1,1-dimethylpropanol (This would imply a 3-carbon chain with two methyl groups on C1, which is not this structure.)
B. 3,3-dimethylpropanol (This would imply a 3-carbon chain with two methyl groups on C3, which is not this structure.)
C. 3-methylbutanol (This is a less specific name for 3-methylbutan-1-ol, but option D is more precise.)
D. 3-methylbutan-1-ol

The most accurate IUPAC name is option D.

The correct answer is $\boxed{\text{D. 3-methylbutan-1-ol}}$.