37. Under section 54EC, capital gains on transfer of land or building or both are exempted if invested in the bonds issued by NHAI & RECL or other notified bond- (a) within a period of 6 months after the date of such transfer (b) within a period of 6 months from the end of the relevant previous year (c) within a period of 6 months from the end of the previous year or the due date for filing the return of income under section 139(1), whichever is earlier (d) At any time before the end of the relevant previous year