The correct phrase to use in the blank space is: A. had cost.
Therefore the sentence will be;
This house had cost 35,000 pounds in 1980.
"Had cost" is used to express the price of the house sometime in the past. It can be used instead of the past tense of cost which is costed.
The past participle form of the verb is used in addition with "had" to create this effect.
Learn more about past participles here:
https://brainly.com/question/14460133
