The correct option is
A unaware of the problems faced by the left-handed people
In the second paragraph, the writer asks the reader to try to handle a pair of scissors and cut a paper using the left hand. And he says that upon doing the same, the reader will know exactly how a left-handed person would feel when using a regular pair of scissors (with his right hand). This tells us that the author feels that right-handed people do not know (or are unaware) of the problems faced by left-handed people. Hence, option A is correct.
Option B is incorrect as there is no mention in the passage about right-handed people being less intelligent than left-handed people.
There is also no mention in the passage about right-handed people being unaware that some people are left-handed. Hence, option C is also incorrect.
'Revenge' is the action of hurting or harming someone in return for an injury or wrong suffered at their hands. According to the passage, the right-handed people have not been hurt or wronged by the left-handed people. Hence, the need for right-handed people to take revenge does not arise. This is not mentioned in the passage either. Hence, option D is incorrect.