Simplifying expressions

This task is about simplifying algebraic expressions.
Circle the correct answer. If you circle (E), write down what the correct answer should be.
 
 
a)

 

 The expression is equal to 

(A)        (B) 2a       (C) 9a       (D) 18a      (E) None of these, = __________

 
 
b)

 

 The expression  is equal to

(A)        (B) 4a       (C) 8a       (D) 12a       (E) None of these,  = __________

 
 
c)

 

 The expression is equal to

(A)         (B)        (C) 6a2     (D) 6           (E) None of these, = __________

 
 
d)

 

 The expression is equal to

(A)         (B) 6        (C) 6a       (D) 6a3       (E) None of these, = __________

 
 
e)

 

 The expression is equal to

(A) 0         (B) 1         (C) 2a       (D) a2         (E) None of these, = __________

 
 
f)

 

 The expression  is equal to

(A) 0         (B) 1         (C) a         (D) 12a       (E) None of these,  = __________

 
 
g)

 

 The expression is equal to

(A)       (B)       (C )        (D) 3a        (E) None of these, = __________