В чем проблема?PyQt5

from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QLabel, QHBoxLayout, QGroupBox, QVBoxLayout, QRadioButton
app = QApplication([])
main_win = QWidget()


RadioGroupBox = QGroupBox("Варианты ответов")
rbtn_1 = QRadioButton('Энцы')
rbtn_2 = QRadioButton('Смурфы')
rbtn_3 = QRadioButton('Чулымцы')
rbtn_4 = QRadioButton('Алеуты')
layout_ans1 = QHBoxLayout()   
layout_ans2 = QVBoxLayout() 
layout_ans3 = QVBoxLayout()

layout_ans2.addWidget(rbtn_1) 
layout_ans2.addWidget(rbtn_2)
layout_ans3.addWidget(rbtn_3) 
layout_ans3.addWidget(rbtn_4)
layout_ans1.addLayout(layout_ans2)
layout_ans1.addLayout(layout_ans3)

RadioGroupBox.setLayout(layout_ans1) 
vert = QVBoxLayout()

vert.setSpacing(5) 
ans = QLabel('Какой национальности не существует')

but = QPushButton('Ответить')


AnsGroupBox = QGroupBox("Результат")
inf = QLabel('Правильно/Неправильно')
res = QLabel('Правильно')
l1 = QVBoxLayout()
l1.addWidget(inf,  alignment=Qt.AlignLeft )
l1.addWidget(res,  alignment=Qt.AlignCenter )

AnsGroupBox.setLayout(l1) 

RadioGroupBox.show()
vert.addWidget(ans,  alignment=Qt.AlignCenter )
vert.addWidget(RadioGroupBox,  alignment=Qt.AlignCenter )
vert.addWidget(AnsGroupBox,  alignment=Qt.AlignCenter )
vert.addWidget(but,  alignment=Qt.AlignCenter )
AnsGroupBox.hide()
def show_result():
    RadioGroupBox.hide()
    AnsGroupBox.show()
    but.setText('Следующий вопрос')
def show_question():
    Radio.GroupBox.show()
    AnsGroupBox.hide()
    but.setText('Ответить')
    RadioGroup.setExclusive(False)
    rbtn_1.setChecked(False)
    rbtn_2.setChecked(False)
    rbtn_3.setChecked(False)
    rbtn_4.setChecked(False)
    RadioGroup.setExclusive(True)


main_win.setLayout(vert)
main_win.show()
app.exec_()

выводит: Could not find the Qt platform plugin "windows" in "" This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem. Уже качал PyQt5