Let us review the answer options -

A - "provisions that provide" is redundant.

B - correct answer. "it" refers to "the new maritime code".

C - "already stimulating ..." is a comma + -ing modifier at the end of a sentence.
It should modify the entire clause as well as apply to the subject of the preceding clause. "already stimulating" then refers to "tiny islets". this usage is clearly illogical.

"large sea areas under provisions of maritime code" suggests that this code applies only to certain sea areas (those under maritime codes). Not the intended meaning.

D - "this" is a demonstrative adjective. You cannot use "this" independently. It must always be used with a noun that it modifies.
For example - this dog, these apples, these facts etc.

Also, the basic structure of D is this -
Because + fact, this (fact) has stimulated ... -> this does not make any sense.

"large sea areas under provisions of maritime code" suggests that this code applies only to certain sea areas (those under maritime codes). Not the intended meaning.

E - this is not a sentence.
"because" is a subordinating conjunction and needs a main clause.
"large sea areas under provisions of maritime code" suggests that this code applies only to certain sea areas (those under maritime codes). Not the intended meaning.