Which of the following systems of equations can be used to find a, the number of adults attending, and s, the number of students attending the game?

The problem can be expressed in the following system of linear equations:
A total of 120 adults (a) and students (s) attended a school:
a + s = 120
Each adult paid $2.50, mathematically, that is 2.5a
Each student paid $1, mathematically, that is 1s
and the total paid by adults and students attending the game was $189
then, we have:
2.5a + 1s = 189
then, we can conclude that the problem can be expressed as follows:
a + s = 120
2.5a + 1s = 189
or equivalently:
a + s = 120
2.5a + s = 189
so, the correct answer is D.