Often attractive and charming, and always inordinately self-confident,

Often attractive and charming, and always inordinately self-confident, people which suffer from antisocial personality disorder demonstrate a disturbing emotional shallowness.

A. people which suffer from
B. people are suffering from
C. people that suffer from
D. people who suffer from
E. people suffer from

people must be followed by 'who'. Thus, eliminate choice A and C.
For choice B and E, people suffer (verb) from... demonstrate (verb). Two verbs together cannot be in the same sentence without any preposition. So there should be relative pronouns. - So eliminate B and E.

Thus, the correct answer choice is D. People who suffer from...

The right answer in my view is option D.

Option A is incorrect because it uses which to refer to people. Which can only modify things and not people.

Option B is incorrect because the use of people are suffering without appropriately modifying the people changes the meaning of the sentence and also makes it awkward.

Option C is incorrect because the use of that to modify people is inappropriate. Who is required.

Option E is also incorrect because people needs to be modified in order to appropriately maintain the meaning of the sentence and avoid ambiguities.

Option D is correct. It rightly corrects the modification error in option A by modifying people rightly with who.

MEANING: often attractive and charming… people WHO suffer from a disorder demonstrate emotional shallowness.

PRONOUNS: when referring to a person, we need "WHO" not "THAT" or "WHICH".

Answer (D)

Error Analysis:

1. "which" can not be used to modify people. It can only modify nouns that are not people.

Process of Elimination:

A. Wrong. As explained in Error Analysis.
B. Wrong. "demonstrate" has no subject.
C. Wrong. "that" can not be used to modify people. It can only modify nouns that are not people.
D. Correct.
E. Wrong. Same error as in option B.

Imo. D

Often attractive and charming, and always inordinately self-confident, people which suffer from antisocial personality disorder demonstrate a disturbing emotional shallowness.

Meaning: People, often attractive and charming, and always inordinately self-confident, that suffer from APD demonstrate a disturbing emotional shallowness

A. people which suffer from - Relative pronoun; which is never used for human beings.
B. people are suffering from - Tense error which leads change in the meaning.
C. people that suffer from - that can be used for things and human beings based on context of the sentence. Here, that refers to those people who have x, y and z characteristics, (Often attractive and charming, and always inordinately self-confident). As people is plural, relative pronoun must be plural, i.e. those. However, such construction seems awkward.
D. people who suffer from - This option can also be considered if C is not available. According to me, who is used with specific name of person or group. However, this option is logically correct though grammatically sounds incorrect. So, hold it.
E. people suffer from - Specific group to general group case, which changes the meaning of the sentence. Hence, usage of relative pronoun is required.

Official Explanation

Correct Answer: D

The pronoun who should be used to refer to people. Choices a and c are therefore incorrect. The clause who suffers from antisocial personality disorder is necessary to describe which people demonstrate a disturbing emotional shallowness. Choices b and e do not use a pronoun to create such a clause, making the sentence unclear and/or illogical.