To quote page 116 of Reichmann's "Cross-Country Soaring" 7th edition,

"The problem is definitely a different one from that of greatest
distance described above. Then we were optimizing for distance; now we
are optimizing for cruise speed: how fast should we fly from thermal to
thermal to realize the best average speed. Since the best cruise
airspeed will result in the best ground-speed as well, there is no need
to calculate the effects of wind."


Tony Verhulst wrote:
.... Best avg XC speed
will be achieved through answer c.

Ok, answer C says "The best lift/drag speed with no regard to wind
velocity.".

So, my best lift/drag speed is 50 knots and I'm flying into a 50 knot
headwind at 50 indicated. And, I'm going ... where? "A" is the correct
answer, IMHO. Answer "A", in the above example, would get you a ground
speed of 25 knots (75 - 50)- you're not going to do much better than
that. The question, though, is poorly worded.

Tony V.