shridhar786
Despite smartphones and easy accessibility for social networks, almost half of the millennials – people reaching young adulthood in the 21st century – are feeling isolated and lonely.
(A) Despite smartphones and easy
accessibility for social networks,
(B) Although
having smartphones and
accessing social networks easily,
[subject? verb](C) Despite
them using smartphones and easily accessing social networks,
(D) Despite their smartphones making access to social networks easy,
(E) Although there is an increasing use of smartphones and easy
accessibility for social networks,
source: wizako.com
The meaning is pretty clear.
Nearly half of millenials feel isolated and lonely even though they have cellphones and access to social networks (and thus might be expected not to feel lonely).
Split #1: Idiom is access TO not access FOR: -- when it is easy for us to connect to something that requires access, the correct idiom is
access to, not
access forOptions A and E incorrectly use accessibility
for. 
Eliminate A and E
Split #2: Although requires a clauseDespite is a preposition that must be followed by a noun or pronoun.
Although is a subordinating conjunction and must be followed by a clause.
In option B there is no subject and no verb.
Instead we see
Although having . . . and accessingWhere is the subject? WHO is "having" (owning) these phones? Who accesses social networks?
-- ___ING words are not working verbs
Option B's "Although" should be followed by a clause with a subject and verb.
Eliminate B
Split #3: Possessive gerunds Option C incorrectly uses THEM in the introduction.
The correct construction is:
Despite their using smartphone and . . . .No kidding. "Them" is 100% wrong.
Very few people know this rule, but a gerund (verbING) is a noun (an action noun, usually).
The pronoun THEM cannot do an action.
These __ING nouns have many verb characteristics.
If we want to show what or who is doing the action in the gerund (verbING), we use the possessive pronoun before the __ING word.
Correct: His shouting at me was a really dumb idea.
Wrong: He shouting at me was a really dumb idea.
Wrong: Him shouting at me was a really dumb idea.
Despite
them using cellphones?
Them is an OBJECT pronoun. Gah. I don't like lingo.
THEM is the word that we use when we say, "Would you like to to meet them?"
THEM is not a subject. Them can't do anything.
Them cannot use or be using cellphones.
As an object pronoun,
them receives action. It does not take action.
Them run errands.

They run errands.
Them hug each other.
They hug each other.
-- what follows "despite" is not a noun phrase because "them" is not connected to
using cell phones.
-- the correct construction is "Despite
their using cell phones. . . ."
HERE is a site that explains how and why gerunds take the possessive case
Eliminate C.
The answer is DDespite their smartphones making access to social networks easier-- despite is followed by a (very long) noun phrase
-- (D)'s logic is good. Although millenials have things that might seem to ease loneliness, millenials still feel lonely.