Final answer:
A butt weld is also known as a fillet weld and is used to join two flat pieces of metal together along their edges.
Step-by-step explanation:
The correct answer is b. Butt weld. A butt weld, also known as a fillet weld, is a type of weld that is used to join two flat pieces of metal together along their edges, resulting in a smooth and continuous joint. It is commonly used in various engineering applications, such as in the construction of bridges, buildings, and pipelines.