Which verb form correctly completes this sentence?
es obvio que acá durante este mes y eso causa avalanchas.
nieve
nievo
nieva
nieven

Nieve = it snows.
nievo = it snowed.
nieva = it's snowing.
nieven = is not a spanish word.
So the correct verb is ' nievo ' 
because " Es obvio que nievo acá durante este mes y eso causa avalanchas."
is translated to " It's obvious that it snowed here during this month, and that caused avalanches" 
Even though "Es obvio que nieve acá durante este mes y eso causa avalanchas" sounds better because in english it would be "It's obvious that it snows here and that causes avalanches" and that makes more sense, but in spanish the first one is correct. 
The answer is "nievo"

1) el chico joven 2) el señor mayor