Answer: b. number of trees
Explanation:
The concept of geometric probability is basically use when we have continuous data .
Since it is impossible to count continuous data , but geometrically ( in form of length, area etc) we can count the outcomes in general to calculate the required probability.
Therefore, from the given options , Option b. "number of trees" would not be used for geometric probability because among all it is the only discrete case which is countable.
Rest of items ( a. area of a rug , c. length of time , d. length of a field) would be used for geometric probability,