Answer:
b . Demanding .
Step-by-step explanation:
The word "assessing/ assess" is the same as making a "guess, estimate evaluate, propose, determine" etc. among others.
Now, considering the given sentence-
The size of the bet showed how confident they were in assessing a home's price.
This means that the people betting were confident of estimating how much the home will cost. And if the word "assessing" is changed to "demanding", then the meaning of the whole sentence changes completely.
Thus, the correct answer is option b.