(a)Mass-size distribution of all sources at different wavelengths. (b) Mass-size. (c) Surface density-mass distributions only for the most massive objects within each clump. The straight line shows the empirical threshold for high-mass star formation (Kauffmann & Pillai 2010). The dashed line shows the result of a linear power-law fit to the whole sample: log (Mass(R_eff)∕M_⊙) = 3.86 + 1.68 × log (R_eff∕pc) (see details in Zhang & Li 2017).