What is the tens digit of the positive integer n ?

There is 1 variable (n) in the original condition. In order to match the number of variables and the number of equations, we need 1 equation. Since the condition 1) and 2) each has 1 equation, there is high chance that D is the correct answer.
In case of the condition 1), the tens-digit of n is always 2. The answer is unique and the condition is sufficient.
In case of the condition 2), from n=19 and 21, the tens-digit is 1 and 2. Hence, the answer is not unique and the condition is not sufficient. Thus, the correct answer is A.

 For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.