A good answer might be:

By writing statements intended to execute in sequence and by not jumping into the middle of them.

Implementing Rule One

Statements automatically execute in sequence. There is no language support for enforcing the single entry/single exit idea. A programmer must consciously follow the rule.

It might look as though the rule could be followed by only jumping to labeled statements. But a statement in the middle of a block might have a label, as in the following: 

start:   ori   $8,$0,4      # $8 = 4
         ori   $9,$0,12     # $9 = 12
midblk:  addu  $10,$8,$9    # $10 = 12+4 = 16
         sll   $10,$10,2    # $10 = 16*4 = 64

         ....

         ori   $8,$0,99     # $8 = 99
         ori   $9,$0,43     # $9 = 43
         j     midblk       # jump to the second statement after start

QUESTION 11:

Is there a syntax for defining code blocks in high-level languages like Pascal, C, or Java?