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Backpatching exists because

  • A.the target machine requires all jumps to be relative
  • B.a jump must be emitted before its destination is known
  • C.the parser cannot determine which production to apply
  • D.temporaries must be renumbered after the code is generated

Answer: B

The destination of a forward jump is not yet known at the moment the jump must be written out. Leaving the field blank and noting where the instruction sits allows the value to be supplied later, which is what makes single pass translation of control constructs possible at all.

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