Explanation:

- Option 1: Bringing

- Incorrect as it suggests a continuous action that cannot be interrupted by being busy.

- Option 2: Bought

- Incorrect since it uses past tense, implying the action was already completed, contradicting the sentence's context.

- Option 3: Had bought

- Incorrect because it uses the past perfect tense, indicating an action completed before another past action, which is not the case here.

- Option 4: Bring

- Correct because it fits the context of something Thomas intended to do but didn’t complete due to being busy.

- Option 5: Was bringing

- Incorrect since it implies an ongoing action that was happening and requires an interruption or incident which isn’t present in the sentence structure.