Concept:This sentence tests the grammatical pattern “too + adjective/adverb + to-infinitive,” which indicates an excessive degree that makes something impossible.
Explanation:The blank must introduce the idea of excess before the given adjective or adverb.
After that adjective or adverb, the sentence contains a “to” infinitive.
Only the word “too” can precede this structure correctly.
For instance, “too tired to continue” shows that the level of tiredness prevents continuing.
“very” and “as” cannot be followed directly by a “to” infinitive in this sense.
“that” would not form the intended “too … to” relation and would need a different clause structure.
Thus, the only word that fits both the meaning and the grammar is “too.”
Answer:A. too