Multiwavelength image of the background system (left: the total system, right: the small central region. Positions of bubbles A (upper right), B (lower left), and C (small in the middle) are overlaid. The HI is summed over the velocity interval: 38.9 km s^-1<v_LSR< 42.2 km s^-1 (left) and 39.8 km s^-1<v_LSR< 42.2 km s^-1 (right), the CO over the interval: 38.6 km s^-1<v_LSR< 41.6 km s^-1 (left) and 38.4 km s^-1<v_LSR< 41.8 km s^-1 (right). Crosses in the CO pictures belong to the BGPS clumps found at the corresponding velocity intervals.