In the center of a desert basin what would one likely find?

if you actually mean basin as in the basin and range province of Nevada. there is no drainage outlet so you would find a dry lake or salt lake in the center, which is not an answer so your prof is pulling your leg. since the center is nearly flat it would be devoid of erosional artifacts, that eliminates everything but d. the dreaded fine grains. however if you look at actual basins in Death Valley and other California desert areas, you will also find fairly large size trigonal rocks. they are somewhat of a mystery and most likely the result wind action which does not require a ground slope to work. so i would have to say none of the above based on experience.