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. 

Ineed you to put up a picture of the map so i can you as much as possible.

In a right-angled triangle: 1- the hypotenuse is the longest side2- we can apply pythagorean rule which states that: (hypotenuse)^2 = (side1)^2 + (side2)^2for the given triangle,longest side is 15 cm  side1 = 9 cmside2 is 12 cm  to check whether the triangle is right-angled or not,compare (15)^2 to the summation of (9)^2 and (12)^in other words, compare 225 to the summation of 81 and 144if they are both equal, then the triangle is right-angles, otherwise, it is not.you haven't provided the diagram showing her work, so i cannot tell the choice. however, apply my explanation to the question you have.