This is a sum of fractions with different denominators.
You can solve them by transforming to fractions with the same denominator.
If you multiply the fraction 2/5 by 2/2 and the simpliy the fraction 2/4 to 1/2 and then multiply it by 5/5 you get:
2/ 5 * 2/2 = 4 / 10
2/4 = 1/2 * 5/5 = 5 / 10
Now you have two fractions with equal denominator which you can sum directly:
4/10 + 5/10 = 9/10
Answer: option D. 9/10