5. A lost in gambling , and as payment executed a promissory note in favor of the winner B. B then assigned the note to C. May C successfully recover from A? 6. Two persons entered into a contract of lease of land. It was stipulated that at any time before the tenant constructed any building thereon, he would cancel the lease Is the stipulation valid? 7. A, B and C are solidarily indebted to D for P 30,000. E however, remitted or renounced A's share. Therefore, on the due date, B paid D only P 20,000. Can B ask for reimbursements from A? Why