Final answer:
Pull-type clutches are used because they require less pedal effort than push-type clutches.
Step-by-step explanation:
The primary reason that pull-type clutches are used is c. Pull-type clutches require less pedal effort than push-type clutches. Pull-type clutches are designed in such a way that the clutch pedal requires less force to engage and disengage the clutch, making it easier for the driver to operate. This is especially beneficial in heavy-duty vehicles where the clutch pedal effort can be quite high.