400×20=8000（米）；
8000米=8千米．
答：沿着400米的跑道跑了20圈是8千米．
故选：C．
Tina, ________ for months to find a job as a waitress, finally worked as a tour guide at a local advertising agency.
A．struggling
B．struggled
C．having struggled
D．to struggle
水下焊割所用设备应定期检查其绝缘性能及（）。
