Who does this shop assistant think he is? He behaves as if he owns the grocery.

Explanation: The phrase "as if" (or "as though") introduces a contrary-to-fact situation. When the preceding clause is in the simple present tense ("He behaves"), the clause following "as if" usually requires the simple past tense or past perfect for a condition contrary to present or past fact, respectively. Here, the current behavior is contrary to the fact that he does not own the grocery, so the simple past "owned" is used to express this unreality/improbability. The Bengali explanation confirms: "as if/as though এর আগে simple present থাকলে as if/as though এর পরে simple past বসে।"