If two communicating entities are in different hosts connected by a network，there is a risk that PDUs will not arrive inthe order inwhich theywere sent ， becausethey may traverse(70)paths through the network. If each PDUs is given a uniquenumber，andnumbersareassigned(71)，thenit isa logicallysimpletaskforthereceivingentityto reorder(72 )PDUsonthebasisofsequence number.Aproblem with this scheme is that，with a(73)sequence number field， sequence number will repeat.Evidently ， the maximumsequence numbermustbe(74)thanthemaximumnumber ofPDUsthatcouldbe outstandingat anytime.
（70）A.same
B.different
C.single
D.Unique
（71）A.randomly
B.equally
C. uniformly
D. Sequentially 
（72）A.received
B.sent
C.transmitting
D.Forwarding
（73）A.various
B.diverse
C.finite
D.infinite 
（74）A.smaller
B.greater
C.less
D.More