The length of one ________ determines how long their______ are.

body part, fingers

The length of one object determines how long their corresponding parts are.

The length of one "thing" determines how long their "things" are.

To determine what "things" are being referred to in the question, we would need more context or specific information. Without that information, it is difficult to provide a precise answer. However, we can still explain how you might go about finding the answer.

To determine the relationship between the length of one "thing" and the length of their "things," you could consider the following steps:

1. Identify the type of "thing" being referred to: Are we talking about living organisms or objects?
2. Determine the specific characteristic or feature of this "thing" that could have different lengths.
3. Find information or research about this specific "thing" and its characteristic related to length.
4. Analyze the available data or evidence to understand the relationship between the length of one "thing" and the lengths of their "things."
5. Draw conclusions or generalizations based on your analysis.

Remember, without more context or specific information, it is challenging to provide a concrete answer.