Choose the past perfect or the past simple. 13. After arriving home, I realised 1 (not / buy) any milk.

{ "answer": "13. After arriving home, I realised I **had not bought** any milk.

**Explanation:**
* 'Realised' is in the past simple. The action of *not* buying milk happened *before* the realisation. Therefore, we need to use the past perfect tense to show what happened first ('had not bought')." }