答案是：
✘ I am busy on my project.
✓ I am busy with my project.

busy 後面如果跟名詞，例如 my project，就應該跟 with，例如：I am so busy with my project.

那如果是跟動詞，就直接跟動詞+ing，例如：I am so busy preparing for the exam.

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