A.±20″√n1+n2 B.±30″√n1+n2 C.±40″√n1+n2 D.±60″√n1+n2
A.±14″√n1+n2 B.±30″√n1+n2 C.±50″√n1+n2 D.±60″√n1+n2
A.5 B.6 C.7 D.8