The correct answer is (b) We eat so that we may live.
Sentence Transformation — Simple to Complex:
Simple sentence with infinitive of purpose (to + V) converts to a Complex sentence using the purpose clause "so that + Subject + may/might/can + V".
Formula: S + V + to + V1 → S + V + so that + S + may + V1
We eat to live → We eat so that we may live. ✓
✗ Option (a): "We eat and want to live" — this is a Compound sentence, not Complex.
✗ Option (c): "so that we could live" — "could" suggests past tense or condition; "may" is correct for present purpose.
✗ Option (d): "Although we eat, we live" — changes the meaning entirely (concession, not purpose).
Source: Wren & Martin — High School English Grammar; BCS Previous Year Questions.