Part 6: Complete each space with one of the words given below. Make changes if necessary
In humankind's milions ( 1 ) ........................ years on earth, many types of erengy resources have been utilised. However, in the last ninety years, petroleum has become by far the most importan. Accounting for over 50 percent of all energy consumed, it is so essential that, without petroleum, we could be faced with ( 2 ) ..................  disaste. Of course, the arth's supply of petroleum will not last forever, and in fact, it will disappear ( 3 ) ............ than most people believe. At the current rate of consumption, the world has proven oil reserves may be ( 4 ) .......................... within forty or fifty years.
 since      ;             soon         ;                late      ;           economic         ;        pollute   ;           exhaust     ;  of