{{B}}quEstions 21—23 ArE BAsED on thE pAssAgE ABout vAnity stAmps. you now hAvE 15 sEConDs to rEAD quEstions 21—23.{{/B}}

whiCh oF thE Following stAtEmEnts is truE ABout thE vAnity stAmpsA．thEy CAn BE usED normAlly to mAil A lEttEr.
B．thEy CAn only BE usED For ExhiBition.
C．thEy ArE usED to AttrACt morE tourists.
D．thEy ArE usED to post on FAmous BuilDings.