After a prolonged illness, Sunita was so weak to walk.
Answer & Solution
Correct option is B
Explanation: The original sentence wrongly uses "so … to". The correlative "so" must be followed by "that" + clause (so weak that she could not walk), whereas "too" is followed by "to" + infinitive (too weak to walk). Option (b) uses the correct "too + adjective + to-infinitive" structure, which already carries a negative sense (she could not walk). Option (a) lacks the verb "was" and wrongly pairs "too" with "that"; option (c) uses "too … so that" and the wrong pronoun "he"; option (d) repeats the original error.
Grammatical rule used: "Too + adjective/adverb + to + V1" expresses excess and has a negative meaning. "So + adjective/adverb + that + subject + verb" expresses result.
Example: He is too tired to work. / He is so tired that he cannot work.
Information Booster: Never use "not" after "too … to", since the structure is already negative (❌ too weak not to walk). Also, "too" should not be used in place of "very" in positive statements (❌ I am too happy to meet you → ✅ I am very happy to meet you).