Creep in belt drive is due to uneven extensions and contractions due to varying tension.

Creep in belt drive is a phenomenon where the belt slips or moves slightly without any external force being applied. This can result in a loss of power transmission efficiency and can cause various issues in belt-driven systems. The correct answer to the question is option 'E', which states that creep in belt drive is due to the expansion of the belt.

Explanation:
Creep in belt drive can occur due to several factors, but the expansion of the belt is one of the primary causes. When a belt is subjected to tension, it tends to elongate slightly. This elongation can be due to the inherent properties of the belt material or the effect of external factors such as temperature changes or moisture absorption.

When the belt elongates, it can result in a change in its length. This change in length can cause the belt to slip or move slightly, leading to creep. The expansion of the belt can be more pronounced in certain materials or in belts with specific properties. Therefore, the material of the belt itself can contribute to creep.

Other factors such as the material of the pulley or the size of the driver pulley can also influence creep to some extent. For example, a larger size of the driver pulley can cause a greater belt wrap angle, increasing the friction between the belt and pulley and reducing the likelihood of creep. However, these factors are not the primary cause of creep.

Uneven extensions and contractions due to varying tension can also contribute to creep. If the tension in the belt is not uniform along its length, different sections of the belt may experience different levels of expansion or contraction, leading to creep. However, this factor is also not the main cause of creep.

In summary, while factors such as the material of the pulley, material of the belt, and uneven tension can contribute to creep in belt drive to some extent, the primary cause of creep is the expansion of the belt itself.