Thanks.
Of the perhaps 200 questions in the meteorology section, there are maybe half a dozen where I cannot understand the answers they show as correct. This is a very commonly used book (Air Pilot's Manual: Air Law & Meteorology, 2015 edition) and I would be surprised if errors persist.
How about a couple more (hope I am not infringing anyone's copyright here?!)
A parcel of air's total water content (vapour +liquid + ice) is important for airframe and engine icing potential. When it cools this potential:
a. increases
b. decreases
c. remains the same <---book's answer
d. evaporates
The wind that blows around curved isobars is called the:
a. curved wind
b. geostrophic wind
c. gradient wind <---- book's answer
d. isobaric wind
For that 2nd one, I wonder if I am confused about terminology. I know the pressure gradient drives the wind flow, and I understand that the Coriolis force then turns it to the right. I understood that the net result of these 2 forces was called the geostrophic wind and it blows more-or-less parallel to the isobars. So I think the answer is b. But I suppose the actual initial airflow is gradient wind??