The desert is than the mountains. a). more dry b). drier

The desert is B. drier than the mountains.
Since the word dry is monosyllabic (meaning that it has one syllable only), you form its comparative form by adding -er to its end. 

Answer(12) judaism; ans(11) all of the above; //ans(10) islands that are artificially created; //ans(9) people accept that the caste system keeps order in society and prevent chaos; ///ans(8),brahman; ans(7) the sikhns; ///ans(6); the non-cooperation movement; asn(5)sporadically grant congressional requests; /ans(4) all of the above; ///ans(3) true; //ans(2) true; //ans(1) false;

The answer would be  b. hope this !