Explanation

Statement (1)

If J is John's age and M is Mark's, then the question stem gives us J = M − 10, and statement (1) gives us M − 5 = 2(J − 5). We have two different equations and two variables, so this statement is sufficient.

The correct answer must be either A or D.

Statement (2)

This gives us M + 5 = 2J. Along with J = M − 10 from the question stem, we have two different equations and two variables, so this statement is sufficient.

**The correct answer is D.**

If J is John's age and M is Mark's, then the question stem gives us J = M − 10, and statement (1) gives us M − 5 = 2(J − 5). We have two different equations and two variables, so this statement is sufficient.

The correct answer must be either A or D.

Statement (2)

This gives us M + 5 = 2J. Along with J = M − 10 from the question stem, we have two different equations and two variables, so this statement is sufficient.