<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <RadioButton android:id="@+id/physic"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="physic"
            android:onClick="onRadioButtonClicked"/>
        <RadioButton android:id="@+id/math"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="math"
            android:onClick="onRadioButtonClicked"/>
</RadioGroup>
<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <RadioButton android:id="@+id/theories"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="theories"
            android:onClick="onRadioButtonClicked"/>
        <RadioButton android:id="@+id/problems_solving"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="problem solving"
            android:onClick="onRadioButtonClicked"/>
</RadioGroup>

public void onRadioButtonClicked(View view) {
        boolean checked = ((RadioButton) view).isChecked();

    switch(view.getId()) {
        case R.id.math:
            if (checked)
                switch(view.getId()) {
                    case R.id.problems_solving:
                        if (checked)
                            showFirstWord("math problem resolution");
                        break;
                    case R.id.theories:
                        if (checked)
                            showSecondWord("math theories");
                        break;
                }
            break;

        case R.id.physic:
            if (checked)
                switch(view.getId()) {
                    case R.id.problems_solving:
                        if (checked)
                            showThirdWord("physic problem solving");
                        break;
                    case R.id.theories:
                        if (checked)
                            showFourthWord("physic theories");
                        break;
                }
            break;
    }
}

private void showFirstWord (String text) {
    Intent first_word = new Intent(this, FirstActivity.class);
    first_word.putExtra("key", text);
    startActivity(first_word);
}
private void showSecondWord (String text) {
    Intent second_word = new Intent(this, SecondActivity.class);
    second_word.putExtra("key", text);
    startActivity(second_word);
}
private void showThirdWord (String text) {
    Intent third_word = new Intent(this, ThirdActivity.class);
    third_word.putExtra("key", text);
    startActivity(third_word);
}
private void showFourthWord (String text) {
    Intent fourth_word = new Intent(this, FourthActivity.class);
    fourth_word.putExtra("key", text);
    startActivity(fourth_word);
}