If You Wanted to Examine If a GABA_B receptor Was

If you wanted to examine if a GABA_B receptor was involved at a specific synapse, which would you use?

A) MK-801, which would inhibit selectively GABA_B receptors
B) Baclofen, which would activate selectively GABA_B receptors
C) Barbiturates, which prolong the postsynaptic current at GABA_B receptors
D) Nicotine, which would enhance the postsynaptic current at GABA_B receptors
E) TTX, which would decrease the presynaptic current at GABA_B receptors