How many pairs (r, r+1) have one or more prime factors common, where r is an integer and 2 ≤ r ≤9 ? Options:	A) 0	B) 1	C) 2	D) 3	E) 4

Rationale: r and r + 1 are consecutive integers . two consecutive integers are co - prime , which means that they do n ' t share any common factor but 1 . for example 20 and 21 are consecutive integers , thus only common factor they share is 1 . answer : a .
Answer: A