Which statement will compute the study day correctly without producing notes for missing values in the log?

Study day is defined as DCMDATE minus RFSTDTC +1

Which statement will compute the study day correctly without producing notes for missing values in the log?
A . STUDYDAY=DCMDATE-RFSTDTC+1;
B . STUDYDAY=input(DCMDATE,yymmdd8.)-input(RFSTDTC,date9.)+1;
C . If RFSTDTC^=” and length(DCMDATE)=8 then STUDYDAY=input(DCMDATE,yymmdd8.)-input(RFSTDTC,date9.)+1;
D . If RFSTDTC^=” and length(DCMDATE)=8 then STUDYDAY=input(DCMDATE,date9.)- input(RFSTDTC,yymmdd8.)+1;

Answer: C