Concept:The correct pattern after "old" in this sentence is
"too ... to", which shows an excessive degree that prevents the action.
Explanation:The sentence is: "The gardener was ..... old to work."
We need a word that fits before "old" and works with "to work" that follows.
The expression "too old to work" means the gardener's age is so great that working is no longer possible.
In this structure,
"too" is always followed by an adjective ("old") and then "to" plus the verb ("work").
For example: "He is too tired to walk."
Option "so" would need a different structure: "so old that he cannot work."
Option "very" only adds emphasis but cannot connect to "to work" correctly.
Option "even" does not fit the grammar or meaning here.
Therefore, the only correct word is
"too".
Answer:C. too