ACAD SINICA,INST HIGH ENERGY PHYS,BEIJING 100039,PEOPLES R CHINA
; UNIV SCI & TECHNOL CHINA,DEPT MODERN PHYS,HEFEI 230026,PEOPLES R CHINA
; ACAD SINICA,INST THEORET PHYS,BEIJING 100080,PEOPLES R CHINA
; CCAST,WORLD LAB,BEIJING 100080,PEOPLES R CHINA
The chiral extension of the minimal standard model makes quarks with two chiralities present parallelly. Some interesting questions, such as the possibility of that the leptons are made of additional leptonic quarks and the proton decay are discussed.