Answer:
a. machine guns; d. rifles
b. Germany's plan to quickly defeat France failed.
Step-by-step explanation:
During WWI, many new technological developments were adopted. This made the war longer, as it became very difficult to win. Machine guns were particularly important among these developments, originally developed by Hiram Maxim. Rifles were also a new addition.
A stalemate occurs when no country can advance, but neither one is retreating either. This means that the war simply continues to exist, without any change in strategy or in conditions. In the case of WI, one of the main reasons for the stalemate was that Germany was unable to defeat France quickly.