求翻译：4. 2011年6月下旬，在中航工业集团直升机研究所参观实习，调研直升机虚拟维修培训系统的开发。是什么意思？

4.2011 in late June, the AVIC helicopter to visit the Institute internship, research helicopter virtual maintenance training systems.

4. * June 2011, late in the aviation industry group visited internship, research institute for helicopter helicopter virtual maintenance training system development.

4. At the end of June, 2011, visits the practice in China National Aviation Corp Industry Group Helicopter Research institute, investigates and studies the helicopter hypothesized service training system development.

4. in late June 2011, the Institute of AVIC group helicopter visit internships, research of helicopter virtual maintenance training system development.