- AMotion
- BLubricant
- CSpeed
- DHeat
Step-by-Step Solution
The relation is cause : the effect it produces. A drought brings on a famine; friction produces heat. 'Motion' is the tempting choice because motion is what friction acts upon — it is the condition friction needs, not what friction produces. A lubricant is the remedy that removes friction, and friction reduces speed rather than causing it.
Answer: D) Heat