Answer:
a. alphabet line
Step-by-step explanation:
Technical drawings are the drawings that help in communicating the designs. These designs are the designs that provide the instruction for the manufacturing of any object. The designs are made with the help of lines and line symbols. Line symbols are termed to be alphabet of lines. They help the designers to draw the designs with accuracy. Various lines are drawn that differ in terms of thickness and darkness. These variations helps the designers to mark the design accurately.