Which describes an example of genetic engineering?
1) by replacing a defective gene, symptoms of a disease disappear.
2)vitamin a is added to rice to combat blindness.
3)two roses are crossbred to create a rose with a certain shade of pink.
4)overtime, the species developed webbed feet

2)Vitamin A is added to rice to combat blindness.

Explanation:

The genetic engineering is a process of manipulation of the genome of the organism by either introducing new genes in an organism's genome or by removing the defective genes. This is basically performed to introduce new traits in an organism or to remove the disease causing genes.

Vitamin A is added to rice to combat blindness is the correct option because genetic engineering will ensure the introduction of the genes which are responsible for secretion of vitamin A in the rice plant as the rice species does not naturally produce vitamin A. This will help in combating the disorder of blindness in humans.  

a is the correct answer