Select the option that can be used as a one-word substitute for the given group of words.
Fertile watery place in a desert

The correct option is Oasis.

Let's break down the meaning of the given phrase and analyze each option:
The phrase "fertile watery place in a desert" refers to an isolated area in a desert that has a water source (such as a spring or well) and supports vegetation.

Now let's look at the definitions of the provided options:
1. Oasis: A fertile area in a desert ecosystem, typically surrounding a water source like a spring or a well. This matches the given group of words perfectly.
2. Obsolete: No longer produced or used; out of date. For example, floppy disks are obsolete technology.
3. Obscure: Not discovered or known about; uncertain or difficult to understand.
4. Ode: A classic form of lyric poetry, typically written in praise of or dedicated to a specific person, object, or event.

Therefore, the word that best substitutes the given phrase is Oasis.