Answer and Explanation:
The articles a and an must be used before singular nouns only. Therefore, if we are talking about a plural noun, no article will be used, and we will fill in the blank with -. Also, it is important to pay attention to the first phoneme of the word immediately after the blank. If the first sound is a consonant sound, than we must use a. If it is a vowel sound, we must use an. Notice that what matters is the sound, not necessarily the spelling.
a) What a deep valley!
b) What - picturesque hills!
c) What a brilliant sky!
d) What a grassy field!
e) What a smooth rock!
f) What - nice parrots!
g) What a fresh air!
h) What - tall trees!
i) What a graceful swan!
k) What - rich flora and fauna!
l) What - attractive surroundings!
m)What a poor vegetation!
n) What a beautiful nature!
o) What an ugly animal!