UNITY - How to make unity wait until i press i key - unity3d

Question

I'm making my very first game in unity. In this game my player is a ball which touches some question marks. When a question mark is triggered it has to display a question and the answers. Till here every thing is fine. Now i need to press a or b according to the question. If the answer is right it will add points. But here is the problem. Unity doesn't wait for me to press the keys. Unity passes through the code before i press the buttons and the game crashes.
void OnTriggerEnter(Collider collider)
{
if (collider.gameObject.CompareTag("QuestionCube1"))
{
Question.text = "Which Number is bigger?";
Answer.text = "A.5 B.10";
if (Input.GetKeyDown(KeyCode.A))
{
gameController.minusQuestion‌​Score();
}
else if (Input.GeyKeyDown(KeyCode.B))
{
gameController.addQuestionSc‌​ore();
}
Question.text = "";
Answer.text = "";
}
}
//Sorry if the code is kinda all over the place I dont know how to pass the code here exactly. The gameController and the UI texts are declared and working

Answer 1

Okay let's shift away from the comment section and let's try to improvise, on my current understandings of your problem.
First thing you must consider is the following.
void OnTriggerEnter(Collider collider)
Triggers ONLY once, when the other collider enters. The solution?
Use OnTriggerStay.
void OnTriggerStay(Collider collider)
This will always check for the input when the objects are colliding.
The next thing to consider is the reset of the text. As far as I understand you should remove it when they are not colliding anymore, so you could have additional method. OnTriggerExit, which will run additional code when they are not colliding anymore.
void OnTriggerExit(Collider collider)
{
if (collider.gameObject.CompareTag("QuestionCube1"))
{
Question.text = "";
Answer.text="";
}
}
So overall
void OnTriggerEnter(Collider collider)
{
if (collider.gameObject.CompareTag("QuestionCube1"))
{
Question.text = "Which Number is bigger?";
Answer.text = "A.5 B.10";
if(Input.GetKeyDown(KeyCode.A))
{
gameController.minusQuestion‌​Score();
}
else if(Input.GeyKeyDown(KeyCode.B))
{
gameController.addQuestionSc‌​ore();
}
}
}

Answer 2

You can use Coroutine to wait for the input after it is triggered.
void OnTriggerEnter(Collider collider)
{
if (collider.gameObject.CompareTag("QuestionCube1"))
{
Question.text = "Which Number is bigger?";
Answer.text = "A.5 B.10";
StartCoroutine(WaitForAnswer());
}
}
IEnumerator WaitForAnswer()
{
for (;;)
{
if (Input.GetKeyDown(KeyCode.A))
{
gameController.minusQuestion‌​Score();
break;
}
else if (Input.GetKeyDown(KeyCode.B))
{
gameController.addQuestionSc‌​ore();
break;
}
yield return null;
}
Question.text = "";
Answer.text = "";
yield return null;
}