Hello. Although you showed the book to which the question refers, you did not say which incident the question refers to, as there are many incidents covered in the book. This makes it impossible for your question to be answered, but I will try to help in the best possible way.
The main factor that points to the transition from old forms of war to new forms of war during the first world war was the use of technologies, mainly those driven by the industrial revolution, which gave the army a warlike power never seen before and allowed each army had access to fighter planes, tanks, submarines, toxic gases and others that did not exist in previous wars and that caused much greater destruction.
The country mouse is warm and generous despite his simple lifestyle.
We brought books,so I hope they will bring
(3.)theirs
its number three because if you stated i hope they will bring their ..... its incomplete
or if you put i hope i bring them ..... its just not sounding right...
In colloquial English 'them" would be acceptable
In formal English 'they' is used accompanied by the corresponding auxilliary verb
So, you could also say Is everyone who works in this store as helpful as they are ?