The relationship between "thrust" and "spear" can be understood by analyzing the function and purpose of each word.

- Thrust: The word "thrust" refers to a forceful forward movement or action, typically done with an object such as a weapon. In the context of this question, it implies a specific type of attack or movement.

- Spear: A spear is a long, pointed weapon that is used for thrusting or throwing. It typically consists of a long shaft with a sharp head at one end. The spear is specifically designed for thrusting actions, making it the most appropriate answer choice.

Relationship:
The relationship between "thrust" and "spear" can be understood through the concept of functionality and purpose.

- Mangle: Mangle refers to the act of severely damaging or mutilating something, often resulting in a twisted or distorted shape. While iron can be mangled, it does not have an inherent relationship with mangle. Therefore, this option does not demonstrate a clear and logical relationship.

- Scabbard: A scabbard is a sheath or case used to hold and protect a sword. While a scabbard is related to a sword in terms of function and purpose, it does not directly involve the concept of thrusting. Thus, this option does not demonstrate a clear and logical relationship.

- Bow: A bow is a weapon that uses tension to propel arrows. While a bow and arrow are related in terms of their function and purpose, the action of thrusting is not directly associated with a bow. Therefore, this option does not demonstrate a clear and logical relationship.

- Fence: Fencing is a sport that involves the use of swords, specifically the epee, to score points by touching the opponent. While "fence" and "epee" are related in terms of the sport, the action of thrusting is not uniquely associated with fencing. Hence, this option does not demonstrate a clear and logical relationship.

Therefore, the correct answer is option D, "fence:epee." The epee is a type of sword used in fencing, and the act of thrusting is a fundamental technique in the sport. This option demonstrates a clear and logical relationship between the words "thrust" and "spear."