Final answer:
Structural factors such as the composition, arrangement, and quality of materials play a crucial role in determining the strength of a structure. Physiological, psychoneural, and environmental factors can also influence strength to varying degrees.
Step-by-step explanation:
The major factor that affects strength is a) Structural. Structural factors such as the composition, arrangement, and quality of materials play a crucial role in determining the strength of a structure. For example, the design and materials used in a bridge will determine its ability to withstand forces and support weight.
While physiological factors (b) such as muscle strength and endurance can also impact an individual's physical strength, in the context of the question, structural factors are more relevant.
Psychoneural factors (c) refer to mental and neural influences on strength, while environmental factors (d) encompass external conditions and influences.