In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.

[EX Q]: A novel membrane sensor for histamine H1-receptor antagonist "fexofenadine".
[EX A]: histamine

[EX Q]: Vitamin A and retinoid signaling: genomic and non-genomic effects.
[EX A]: retinoid

[EX Q]: Synthesis, radiosynthesis, and biological evaluation of carbon-11 labeled 2beta-carbomethoxy-3beta-(3'-((Z)-2-haloethenyl)phenyl)nortropanes: candidate radioligands for in vivo imaging of the serotonin transporter with positron emission tomography.
[EX A]:
serotonin