Questions: Which of the following is a highly compact structure that is very commonly used to transition from one region of secondary structure to another in a globular protein?

The answer is (B): $\beta$ turn.

Explanation for each option: (A) $\alpha$ bend: This is not a commonly recognized term in protein structure. The term "bend" is not typically used to describe a specific secondary structure transition in proteins. (B) $\beta$ turn: This is a highly compact structure that is very commonly used to transition from one region of secondary structure to another in a globular protein. $\beta$ turns allow the polypeptide chain to reverse direction, which is essential for the compact folding of globular proteins. (C) $\alpha / \beta$ hairpin: This term is not commonly used in the context of secondary structure transitions. Hairpins generally refer to specific loop structures, but the term "alpha/beta hairpin" is not standard. (D) High-glycine loop: While glycine-rich loops can be flexible and are found in some proteins, they are not specifically known for being a common structure used to transition between secondary structures. (E) None of the above: This is incorrect because option (B) $\beta$ turn is a correct and commonly used structure for transitioning between secondary structures in globular proteins.

Summary: The correct answer is (B): $\beta$ turn, as it is a highly compact structure commonly used to transition from one region of secondary structure to another in a globular protein.