Correct Answer - D
In given problem, disease is the result of sex-linked recessive genes. As neither man nor woman shows signs of disease it means woman would be carrier for disease. In their children non of the daughters suffer from disease, while the sons were suffered, it means daughters are also carrier (i.e. X-linked recessive).
Suppose, genotype of man = X Y
Genotype of woman = `X^(d) X`
(d-disease causing gene)
For each delivery the probability for each combination is 25%. So, among seven children 2 normal daughter, 3 diseased sons and 2 normal sons are possible.