Evolution of L_[CII], L_FIR, and L_[CII]/L_FIR (from left to right) as a function of t_sf. The four clouds are represented with different colours and the three LOS with different symbols; the highly time-resolved datapoints along the x − y-projection for MC1-HD and MC2-HD are connected with a line. Overall, we observe a general tendency of a decreasing L_[CII]/L_FIR with increasing t_sf. There is, however, some scatter in the values for different clouds at a given t_sf, which we attribute to different star formation activities. We note the logarithmic y-axis scale in the right panel.