Answer:
D. 10
Explanation:
The greatest common factor of any two or more numbers is the highest number that divides them exactly (meaning it leaves no remainders).
Having that in mind, we need to find the greatest number which is both a factor of 80 and 70.
As can be seen above the greatest number both divisible by 80 and 70 is 10; therefore, the GCF of the two numbers is 10.