A good answer might be:

A null (zero) is placed in the link field of the last node. (Actually, for SPIM, a zero is already there. But with a real OS where dynamic memory is both allocated and deallocated you must be sure to zero the link.)

Last Link

Now the linked list has been constructed. The field first points to the first node. Here is some code from the previous chapter. The code traverses a linked list, printing out the data found at each node. 

          _____  ___,_______    # get a pointer to the first element
          
lp:       beqz   $s0,endlp      # while the pointer is not null
          lw     $a0,0($s0)     #   get the data of this element

                                #   do something with the element
          li     $v0,1          #   print it
          syscall               #
          la     $a0,sep        #   print separator
          li     $v0,4          #
          syscall               #
          
          lw     $s0,4($s0)     #   get the pointer to the next element
          b      lp
          
endlp:     . . . 

          .data
first:    .word  0
sep:      .asciiz "  "

Our new linked list has the same form as the previous chapter's linked list. This code will work fine.

QUESTION 15:

But, those blanks... Fill them in.