Hello, the answer of suspho is correct but here is another procediment:
You prime factor 10 and 8... 10 = 2*5 and 8 = 2³
√2*5 * √2³
Let's take 2³ out of the square root. The radicand has a bigger exponent than the index (2) but you can't divide 2 by 3 so we write √2² * 2 and we can finally take out only 2²
√2*5 * 2√2 and multiply all the radicands.
2√20 and prime factor 20... 20 = 2²*5 and take 2² out
2√2² * 5 = 2*2√5 = 4√5
Answer B