7 letters have to be put into their 7 respective envelopes. If the letters are inserted randomly into the envelopes, what is the probability that all the letters go into their respective envelopes?
Select the correct option:  A) 1/30  B) 1/720  C) 1/5040  D) 1/240  E) 3/5
A-B-C-D-E (envelopes)   a-b-c-d-e (letters)   7 letters (a, b, c, d, and e) can be assigned to 7 envelopes (arranged) in 7! ways, out of which only one will be correct, thus the probability is 1/7! = 1/5040.   Answer: 1/5040.
<result>C</result>
7 letters have to be put into their 7 respective envelopes. If the letters are inserted randomly into the envelopes, what is the probability that all the letters go into their respective envelopes?