The questions connected with Android Studio : I hope for a ponimayeniye, a beginner.
I can't solve these two problems:

1.Error:(20, 20) error: cannot find symbol variable mQuestionBank
2.Error:(20, 20) error: cannot find symbol variable mQuestionBank


Code:

    enter code here
`enter code here`import android.os.Bundle;
`enter code here`import android.support.v7.app.AppCompatActivity;
`enter code here`import android.widget.Button;
`enter code here`import android.widget.TextView;
`enter code here`import android.widget.Toast;

public class QuizActivity extends AppCompatActivity {

    private android.widget.Button mTrueButton;
    private android.widget.Button mFalseButton;
    private Button mNextButton;
    private TextView mQuestionTextView;

    private int mCurrentIndex = 0;

    private void updateQuestion() {
        int question;
        question = mQuestionBank[mCurrentIndex].getQuestion();
        mQuestionTextView.setText(question);
    }

    private void checkAnswer(boolean userPressedTrue) {
        boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();

        int messageResId = 0;

        if (userPressedTrue == answerIsTrue) {
            messageResId = R.string.correct_toast;
        } else {
            messageResId = R.string.incorrect_toast;
        }
        Toast.makeText(this, messageResId , Toast.LENGTH_SHORT)
                .show();
    }

    private TrueFalse[] mQuesionBank = new TrueFalse[] {
            new TrueFalse(R.string.question_1, false),
            new TrueFalse(R.string.question_2, true),
            new TrueFalse(R.string.question_3, false),
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        mQuestionTextView = (TextView)findViewById(R.id.question_text_view);

        mTrueButton = (android.widget.Button)findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new android.view.View.OnClickListener() {
            @Override
            public void onClick(android.view.View v) {
                checkAnswer(true);
            }
        });

        mFalseButton = (android.widget.Button)findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new android.view.View.OnClickListener() {
            public void onClick(android.view.View v) {
                checkAnswer(false);
            }
        });

        mNextButton = (Button)findViewById(R.id.next_button);
        mNextButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
                updateQuestion();
            }
        });

        updateQuestion();

    }
}




I will be very grateful to those who will intelligibly and it is clear explain! Thanks!
Sorry, if has issued something not so. First time ;)