instruction:
In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.
question:
The undulating courses of two rivers , the Hondo and the Sarstoon River , define much of the course of the country 's northern and southern boundaries .
answer:
The Hondo and the Sarstoon River make the northern and southern border .


question:
In conventional usage , boredom is an emotional and occasionally psychological state experienced when an individual is left without anything in particular to do , is not interested in their surroundings , or feels that a day or period is dull or tedious .
answer:
Boredom is an emotional state that comes when a person has nothing to do , and is not interested in anything .


question:
In air forces , the serial number is used to uniquely identify individual aircraft and is usually painted on both sides of the aircraft fuselage , most often in the tail area , although in some cases the serial is painted on the side of the aircraft 's fin / rudder ( s ) .
answer:

It is usually painted on both sides of the aircraft , most often in the tail area , although in some cases the serial is painted on the side of the aircraft 's fin / rudder ( s ) .