Definition: In this task, you are given a sentence. You are expected to write the name of the organism substances in the body mentioned in the input. Although there might be several correct answers, you need to write one of them.
Input:  Cerebral blood flow ( CBF ) was measured with continuous arterial spin - labeling perfusion magnetic resonance ( MR ) imaging in 14 children with sickle cell disease and seven control subjects .
Output:
blood