Final answer:
The upper arm is chosen when a specific branch of a body part does not have its own value.
Step-by-step explanation:
The body part that is chosen when a specific branch of a body part does not have its own body part value is the upper arm. In anatomical terms, the term 'brachium' is used to refer to the upper arm. Similarly, for the lower arm, the term 'antebrachium' is used. These specific terms help increase precision and clarity when describing different regions of the body.