Correct Option: B

We know that Greatest n digit number which when divided by three numbers p,q,r leaves no remainder will be Required Number = (n – digit greatest number) – R , R is the remainder obtained on dividing greatest n digit number by L.C.M of p.q,r.
LCM of 10, 15 and 20 = 60
Largest 4-digit number = 9999

∴ Required number = 9999 – remainder = 9999 – 39 = 9960