Final answer:
The correct spelling word for the sentence provided is 'rein,' which is the strap used to guide a horse. This term relates to the examples provided where characters are engaged in horseback riding and potentially using reins to control their horses.
Step-by-step explanation:
The correct spelling word to complete the sentence 'Bill pulled on the left rein to make the horse change direction' is 'rein.' When discussing the means by which a rider communicates with and directs a horse, 'rein' is the strap attached to the bit and used to guide the horse. In the provided texts, there are numerous references to horseback riding and controlling horses, which ties in with the concept of using reins to direct a horse's movement.
For example, 'Venters rode to the barn, and, leaping off, shouted for Jerd. The boy came run-ning' illustrates a scene involving horse riding where reins could be involved. Similarly, 'The Masked Rider huddled over his pommel slowly swaying to one side' suggests a rider atop a horse who may also be using reins to maintain balance or direct the horse.
Understanding the spelling and use of 'rein' is also important when considering phonetics as mentioned in the texts with examples such as 'ball' [bol] and 'ballot' [bálət], which elucidate how the placement of letters can affect pronunciation.