Final answer:
To factor the expression 10ab + 5a by factoring out the greatest common factor, we can write it as 5a(2b + 1).
Step-by-step explanation:
To factor the expression 10ab + 5a by factoring out the greatest common factor, we need to find the largest number or variable that divides evenly into both terms. In this case, the greatest common factor is 5a. So we can write the expression as:
10ab + 5a = 5a(2b + 1)
Therefore, the correct answer is A) 5a(2b + 1).