Political scientist: As a political system, democracy does not promote

Let us talk about conditional statements -

If X happens, then Y happens. I can write this as - X --> Y.
Here X is the sufficient condition and Y is the necessary condition.
Why is X called the sufficient condition? If X happens, then it is sufficient for Y to happen.
Also, note that when X happens, Y does necessarily occur. i.e. Whenever X happens, Y always happens.
Consequently, If Y does not happen then X also cannot happen. i.e. Not Y --> Not X.

Let me illustrate this with a simple example - If it rains, then there will be a traffic jam.
Rains --> Traffic Jam.
Here, 'rains' is the sufficient condition. This means that WHENEVER it rains, there will be a traffic jam.
'traffic jam' is the necessary condition. Consequently, If there is NO traffic jam, it cannot rain.
Also, note that traffic jam --> may or may not mean rains. (Traffic jams can occur because of other reasons - strikes, processions etc.)

Let us now look at the argument -
Premise 1 - Some Democracies --> No political freedom (most oppressive societies)
Premise 2 - Political Freedom --> Some despotisms and oligarchies (No democracy).
Conclusion - Democracy --> Does not promote freedom.

Let us again look at Premise 1 and this argument - Democracy --> Political Freedom.
From this, we know that Democracy is not a sufficient condition for Political Freedom. If it were, Premise 1 would be incorrect.

Let us look at Premise 2 and this argument - Political Freedom --> Democracy
From this, we know that Democracy is not a necessary condition for Political Freedom. If it were, Premise 2 would be incorrect.

Based on these two, the author makes the conclusion that democracy does not promote freedom.

A - the author does not confuse necessary and sufficient conditions in his/her argument. All we know from the premises is that democracy is neither sufficient/necessary for political freedom.
Also, note that the author's conclusion (Democracy does not promote freedom) does not mention if any conditions are necessary/sufficient to bring about political freedom.

B - look at this argument - Democracy --> Freedom. (The author's conclusion is trying to weaken this argument.)
One way to weaken this argument is through reverse causation.
That is by saying that Freedom --> Democracy
B weakens the argument above through this. Hence, it acts as a strengthener to the author's argument.

C - is incorrect. Note that the premises 1 and 2 are very much relevant to the author's argument.
The states that based on premises 1 and 2, democracy is not sufficient/necessary for political freedom. Hence, it does not promote political freedom.

D - correct answer. The argument ignores the possibility that even if democracy is not sufficient/necessary for political freedom, it can still support political freedom.
Premise 1 states Democracy is not sufficient for political freedom. This does not mean that Democracy does not support political freedom. For example - there might be other factors (such as a deeply theocratic society) that might prevent Democracy from guaranteeing political freedom.

Premise 2 states that Democracy is not a necessary condition for political freedom. Does not mean that democracy does not promote freedom. There might be other factors (such as a secular constitution, powerful court system) that can guarantee freedom in the absence of democracy.

E - The historical examples given are facts, not the author's personal points of view.

Hope this helps