What makes the deep web distinct from the surface web?

a$.$

The surface web consists of content that is indexed by search engines such as Google, whereas the deep web consists of pages that are not indexed by such search engines.

b$.$

Despite perceptions to the contrary, the deep web generally offers greater transparency and uniformity than the surface web. Therefore, serious researchers prefer not to use the surface web at all, but to instead rely on the deep web for primary sources.

c$.$

The deep web reduces the complexity of the surface web through an intricate filing system that resembles the set$-$up of an SQL server. On the surface web, no such cataloging$/$organization exists.

d$.$

On the deep web, criminals can engage in illicit activities without needing to worry that federal agents might be monitoring their activities; on the surface web, however, criminals should assume that they are being routinely monitored.