Answer:
a. The domestic car market showed an <em><u>impressive</u></em> growth of 50 % for three consecutive years from 2001 to 2003.
b. The domestic car market grew <em><u>impressively</u></em> by 50% for three consecutive years from 2001 to 2003.
Explanation:
In the given question, the word to be used in the blanks depends on the structure of the sentence. While an adjective describes a noun, an adverb describes or modifies a verb.
Now, the given sentences will use the same word in their adjective and adverb form. And the pair of words to use in the two sentences are-
a. The domestic car market showed an <em><u>impressive growth</u></em> of 50 % for three consecutive years from 2001 to 2003.
b. The domestic car market grew <em><u>impressively</u></em> by 50% for three consecutive years from 2001 to 2003.