Alfred is practicing typing. The first time he tested himself, he could type 45 words per minute. After practicing for a week, he could type 48 words per minute. After two weeks he could type 51 words per minute. Based on this pattern, predict how fast Alfred will be able to type after 4 weeks of practice.
 A. 
61 words per minute 
 
 B. 
57 words per minute 
 
 C. 
54 words per minute 
 
 D. 
51 words per minute