Given the task definition and input, reply with output. You are given a short paragraph, a question and two choices to answer from. Choose the correct answer based on the paragraph and write the answer(not the key).

Paragraph: At higher concentrations, particles of reactants are crowded closer together, so they are more likely to collide and react.
 Question: Mike is watching how particles of reactants function, and sees that they are crowded very close. Considering that the concentration of them is very high, the chance of them colliding together is 
 Choices: A)high 
B)low
high