💡 Detailed Explanation
The grammar pattern '〜はずだ' (hazu da) expresses a strong expectation or logical conviction based on reliable evidence (should be the case / I am sure that...). Option 1 is correct: 'It should rain tomorrow (according to the forecast, etc.), so let's bring an umbrella.' Option 2 is incorrect because personal career decisions of the speaker ('I will become a doctor') are expressed using 'つもり' (intention) or '予定' (plan), not 'はず'. Option 3 incorrectly uses 'はず' for a mechanical condition (should be '押すと'). Option 4 'はずでした' implies regret/contrary-to-fact situation, but in this specific context it doesn't function well as a correct usage example compared to option 1.