chất mẫu chuẩn 
reference substance [ chất ] : matter, material, substance, matter, agent
[ mẫu ] : (1) hectare (c. 3600 sq. meters); (2) model, pattern, sample, form, specimen
[ chuẩn ] : to agree, approve, allow; standard
Most Common Compounds Set 1:
Most Common Compounds Set 2 :