Method that takes user input and returns a string value get's stuck

Question

Well as I said in the title, I have a method that when's called should take user input and return another string value based on that input. For example: User inserts "A" and the method returns "a". I made it work once, but then when I try to change user's input it get's stuck and requires the user to repeat the same input.
class TakeDecision{
public string Choose(){
string decision = Console.ReadLine();
string x = (decision == "A")? "a" : (decision == "B")? "b" : "wrong letter";
return x;
}
}
public static void Main(string[] args){
TakeDecision dec = new TakeDecision();
if(dec.Choose() == "a"){
Console.WriteLine("a);
//--Here's the issue
//--When I type "B" in the console it seems like it starts the Choose() method once more
//--The second time I write "B" it works.
if(dec.Choose() == "b"){
Console.WriteLine("b");
}
}
}

Answer 1

// If statement has to be clear made
TakeDecision dec = new TakeDecision();
string si = dec.Choose();
if(si == "a"){
Console.WriteLine("a");
}

Answer 2

Ohh thanks, I'm going to try it soon. I didn't thought that by calling the method directly it would cause this issue. I hope this solved my problem ;D.

Tried it.. it doesn't work. It goes directly after the if statement..