To find the least common multiple of several numbers, start by finding the prime factorization of each number:

4 = 2^2

5 = 5

6 = 2 x 3

7 = 7

8 = 2^3

9 = 3^2

10 = 2 x 5

The least common multiple will contain every prime factor, so there must be a 2, a 3, a 5, and a 7 in the result. To find the exponent, look for the largest exponent among the factorizations. For instance, there is a 2 in the factorizations of 4, 6, 8, and 10. The largest exponent is 2^3, the factorization of 8. Thus, the least common multiple will contain 2^3. That limits our choices to (A) and (B).

The largest exponent of 3 is 3^2, in 9. The only exponents of 5 and 7 are 1, so the answer we're looking for is (A), (2^3)(3^2)(5)(7).v