The sea wave continue to … the cliff on the west coast constantly

Step 1: Analyze the question The sentence says sea waves continue to __ the cliff on the west coast constantly. We need a verb that describes what waves do to a cliff over a long period.

Step 2: Explain the concept This is a question of word choice (lexis and collocation). Some words may seem close in meaning, but only one fits the natural pairing of "waves" and "cliff".

Step 3: Test each option

• A. impair means to weaken or damage the quality of something, such as hearing, vision or health. It is not used for physical features like cliffs.
• B. rub means to apply friction lightly. Waves do rub against rocks, but "rub the cliff" doesn't convey the lasting damage the sentence suggests.
• C. knock means to hit sharply. It is not a natural word for the slow, continuous action of waves.
• D. erode means to gradually wear away rock or soil through water, wind or ice. This matches "continue to ... constantly", which points to a slow, repeated process.

Step 4: Answer The correct option is D. erode. Constant wave action wears away cliffs over time, which is coastal erosion, a topic you will also meet in Geography.

Step 5: Exam tip When you see natural forces (water, wind, waves) paired with land features (cliffs, soil, rocks), think erode. Also, words like "constantly" and "continue to" hint at a gradual process, which is the core meaning of erosion.