The following sentence has been divided into parts. One of them may contain an error.
It was that cold / that I could not feel / my fingers at night.

Correct option is A

Option (a) contains an error.
Explanation: The phrase “It was so cold that I could not feel...” is the correct structure for showing cause-effect using intensifiers.
Grammatical Rule Used:
“So + adjective + that + result clause” is used to express the consequence of a condition.
Example: It was so hot that we had to cancel the match.
�� Information Booster: "That" is used to connect result clauses but must be preceded by intensifiers like so, such, etc.