#include <QApplication>
#include <QWidget>
#include <QGroupBox>
#include <QVBoxLayout>
#include <QComboBox>

class MyWidget : public QWidget {
public:
    MyWidget() {
        QGroupBox* groupBox = new QGroupBox(this);
        QVBoxLayout* groupBoxLayout = new QVBoxLayout(groupBox);

        QComboBox* combo = new QComboBox(groupBox);
        combo->addItems(\{"Option 1", "Option 2", "Option 3"});
        groupBoxLayout->addWidget(combo);

        QVBoxLayout* layout = new QVBoxLayout(this);
        layout->addWidget(groupBox);
    }
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    MyWidget window;
    window.show();
    return app.exec();
}