The word **迅速 (jinsoku)** is the correct choice. It is a na-adjective meaning 'prompt,' 'speedy,' or 'swift.' It perfectly captures the nuance of acting quickly and efficiently without delay, which is crucial in contexts like business correspondence (e.g., a prompt reply) or emergency response (e.g., a speedy evacuation). It's a formal word often used in written or official language, making it ideal for the JLPT N2 level. * Example: お客様からの問い合わせには、**迅速な**対応が求められる。(A prompt response is required for customer inquiries.) * Example: 災害時には**迅速な**避難が重要です。(Speedy evacuation is important during a disaster.) Common Mistakes / Nuances: ❌ : This word means 'immediately' or 'right away,' but it functions as an **adverb**, not a na-adjective. Therefore, it cannot modify a noun with な. You use it to describe when an action starts, often at the beginning of a sentence. It expresses the immediacy of starting something. * *Correct use:* ご注文の品を**早速**お送りします。(We will send your order right away.) * *Incorrect grammar:* ×早速な対応 (sassoku na taiou) ❌ : This means 'rapid' or 'fast' and is used to describe the **speed of a change or development**, not the promptness of an action taken by a person or organization. It implies a significant change happening over a short period. It focuses on the velocity of a process. * *Context:* It's often paired with words like 発展 (development), 成長 (growth), or 悪化 (worsening). * *Example:* 日本は戦後、**急速な**経済成長を遂げた。(Japan achieved rapid economic growth after the war.) ❌ : This is an **i-adjective** meaning 'quick,' 'nimble,' or 'agile.' While it can describe a quick action, it often emphasizes physical speed or quick reflexes. **迅速 (jinsoku)** is a more formal, Sino-Japanese (漢語) term preferred in business or official contexts, whereas **素早い (subayai)** is a native Japanese word (和語) that can sound slightly less formal. * *Context:* Often used for physical movements or quick judgments. * *Example:* 泥棒は**素早い**動きで逃げていった。(The thief escaped with quick movements.)

正解は **迅速 (jinsoku)** です。これは「物事の処理や行動が非常に速いこと」を意味するナ形容詞で、「prompt」「speedy」「swift」のニュアンスに最も合致します。ビジネス上のやり取り（例：迅速な返信）や緊急時の対応（例：迅速な避難）など、遅れることなく効率的に行動することが求められる状況で使われる、やや硬い表現で、JLPT N2レベルにふさわしい単語です。 * 例文：お客様からの問い合わせには、**迅速な**対応が求められる。 * 例文：災害時には**迅速な**避難が重要です。 Common Mistakes / Nuances: ❌ : This word means 'immediately' or 'right away,' but it functions as an **adverb**, not a na-adjective. Therefore, it cannot modify a noun with な. You use it to describe when an action starts, often at the beginning of a sentence. It expresses the immediacy of starting something. * *Correct use:* ご注文の品を**早速**お送りします。(We will send your order right away.) * *Incorrect grammar:* ×早速な対応 (sassoku na taiou) ❌ : This means 'rapid' or 'fast' and is used to describe the **speed of a change or development**, not the promptness of an action taken by a person or organization. It implies a significant change happening over a short period. It focuses on the velocity of a process. * *Context:* It's often paired with words like 発展 (development), 成長 (growth), or 悪化 (worsening). * *Example:* 日本は戦後、**急速な**経済成長を遂げた。(Japan achieved rapid economic growth after the war.) ❌ : This is an **i-adjective** meaning 'quick,' 'nimble,' or 'agile.' While it can describe a quick action, it often emphasizes physical speed or quick reflexes. **迅速 (jinsoku)** is a more formal, Sino-Japanese (漢語) term preferred in business or official contexts, whereas **素早い (subayai)** is a native Japanese word (和語) that can sound slightly less formal. * *Context:* Often used for physical movements or quick judgments. * *Example:* 泥棒は**素早い**動きで逃げていった。(The thief escaped with quick movements.)