You use 'an' before words that start with a vowel (or a vowel sound), and 'a' before any other word.
So in your example, it's 'AN energy crisis'.
Yes, economy is an adjective in the term 'economy crisis'.
the nullification crisis
Crisis is a noun. As an adjective, when referring to, or for the use in dealing with a crisis
menopause
Solutions to the climate crisis mean a solution to other problems
menopause
Brinkmanship.
On example of when one has to deal with a crisis is when there is a house fire. One must get to safety, get their loved ones to safety, and then rebuild their life after the fire.
The Syrian crisis is getting out of hand.Excuse me Mr Prime Minster, but we have a crisis on our hands.The nuclear crisis was the beginning of the end of the world.
Well the word "Crisis" can be used quite broadly. A crisis for a student, for example, is when his dog eats his homework. A crisis for a techie could be his computer crashing. Or for a stockholder, when the stocks crash.
all
The plural of crisis is crises.Two example sentences are:The British government discussed in a meeting about how the two crises should be handled.The tsunami caused several crises in several countries.