Write down the answer to the previous question and then answer the following question.

23. A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is
(a) 1/2 m/s.
(b) 2/5 m/s.
(c) 5/6 m/s.
(d) 6/5 m/s.
(e) 1 m/s.