These indentations are called coffers.
Source B is more credible because it is from a government site, so it is meant to inform. It has a quote that shows drones are in debate.
At first look, the sources seem similar. They both were written around the same period and the URL appears almost identical. However, it is important to notice that source A is from a website ending in ".net," while source B ends in ".gov." Government websites are always more credible than a website ending in ".com" or ".net." Also, source A has advertisements, which means it is mostly for entertainment. In comparison, source B has a quote from President Obama. Since the research is about the invention of drones and their controversial uses, source B is also more helpful since the title specifically mentions the rules and misuse of drones.
I believe it was in the 1930's.
