I'm not too clear on the definition of a choke point, but...
A is a very important spot; it is the only light orange territory to border more than one Asian territory, and it borders two red and three blue territories. It's the key territory that separates Scandanavia and Western Russia from Asia.
B,C,D, and to a lesser extent E are all sort of choke-points, in that there's no easy way to go around them. E's a funny one because it's in the middle of a bonus.
I'm not sure about F; it hasn't been a key territory in any game I've played. Both the green and blue bonuses are quite hard to defend from each other, and the blue bonus also is inefficient.
Edit: C and D are basically each 1/2 of a choke point, with the other half on the other side of the water. B is stronger than it's Middle Eastern counterparts, but if it's ever the only way you have of getting into Asia, you're probably in trouble.
In real terms a choke point is where you fight in a restricted, usually narrow area. Mostly utilized by smaller forces looking to reduce the numbers a larger force can bring to fight. Taking away their main advantage.
The most famous usage in military history would be The Thermopylae pass. An army badly in need of one would have been Lee's Army of Northern Virginia which was eventually defeated by Grants continous expanding of the front reducing the amount of men Lee could focus in one place to defend against a break through.
In Warlight terms it means:
nounNORTH AMERICAN a point of congestion or blockage. "the tunnel is a choke point at rush hour"
It's one territory that your opponent has almost no choice but to go through.
So as important as A is it's not a choke point, you can just go around it and threaten the bonus(es) that way and you can do it quickly.
B is a choke point because the only other way into Africa from the Middle East is via a 5 turn detour through southern Europe.
C is a double choke point as it blocks access to Africa from South America and vice versa.
D is a choke point but the territory south of it is a better one. If you can afford to lose the bonus.
E is a minor choke point from the north, it's only 3 turns to get around. But a better one if you're defending the north.
I wouldn't really call F a choke point.
Other choke points are:
Iceland or Sweden, Morocco or Spain, Alaska, South Africa and Iran in the ME