What is an erg, and what challenges do they pose for people?

In the text it stated "Sand seas are called ergs," and "An erg is a desert area where sand accumulates and is blown into sand hills, called dunes."  Erg pose a challenge by is that when they form a sand dune it is harder for the people to cross so the Sahara must avoid them which can waste time and resource.

Explanation:

I feel bad for you bro after 3 years lm.ao

after balancing the chemical equation, what are the coefficients for these compounds?

h2s      

⇒ 3

hno3    

⇒ 2

works for edg

well since twins have about the same dna they dont have one think in common which is the figer print. nobodys fingerprint is the same. if your using twin you would most likely get around the same results for both of them because of the genetics.. i hope this