Fill in the blank with appropriate option.The old garage suddenly collapsed one day. Luckily, the owner wasn't there or he _ received serious injuries.

Explanation

The correct answer is 'could have' as it accurately expresses a hypothetical possibility in the past. The garage collapse suggested a scenario where the owner might have been injured, which didn't happen. 'Might as well' suggests a present or future decision without serious consequence, 'have to' indicates obligation, and 'would' suggests a conditional future or habitual past action, none of which appropriately convey the intended past hypothetical situation.