Task: Sentence Ordering
Input (English): Steps: (1) These pores are called stomata (2) Water is absorbed by the roots (3) It passes through vessels in the stem on its way to the leaves (4) Sunlight is absorbed by a green chemical in the leaves.  
Where does the following step fit into the given list of steps: Carbon dioxide from the air passes through small pores (holes) in the leaves 
Output (English):  Before step 1.