Step 1: Understand the context. Mei Ling is 'so exhausted' — very tired — after a long swim. The word in the blank must describe how someone who is completely tired falls into bed. Step 2: Test each option. - tumbled: suggests accidental, rolling fall — not from exhaustion - rolled: horizontal surface movement — does not fit - stumbled: tripping while walking — does not fit getting into bed - collapsed: to sink down suddenly due to tiredness or weakness — fits perfectly Answer: collapsed