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The number of constituent quarks (NCQ) scaling for hadrons and the number of constituent nucleons (NCN) scaling for light nuclei are proposed for nuclear modification factors ( R c p ) of hadrons and light nuclei, respectively, according to the experimental investigations in relativistic heavy-ion collisions. Based on the coalescence mechanism the scalings are performed for pions and protons at the quark level, and for light nuclei $d(\bar{d})$ d ( d ¯ ) and 3He at the nucleonic level, respectively, formed in Au+Au and Pb+Pb collisions, and a nice scaling behaviour emerges. The NCQ or NCN scaling law of R c p can be, respectively, taken as a probe for the quark or nucleon coalescence mechanism for the formation of hadron or light nuclei in relativistic heavy-ion collisions.