Step 1: Understanding the Concept:
This question tests knowledge of phrasal verbs with 'Keep'. The sentence is an imperative (a command), often seen on signs.
Step 2: Detailed Explanation:
Let's look at the meanings of the phrasal verbs:
- Keep off: To stay away from something; to not touch or walk on something. This is commonly used in signs like "Keep off the grass."
- Keep on: To continue doing something. (e.g., "Keep on trying.")
- Keep up: To maintain a certain pace or level. (e.g., "Keep up the good work.")
- Keep away: To maintain a distance from something, often for safety. (e.g., "Keep away from the fire.")
The context of "the grass" strongly suggests a command not to walk on it. The most appropriate phrasal verb for this is "Keep off".
Step 3: Final Answer:
The correct option is (A) because the phrasal verb "Keep off" means to avoid walking on a particular area.