In Their Classic Experiments to Determine the Electrical Properties of Neurons

In their classic experiments to determine the electrical properties of neurons, Hodgkin and Huxley used

A) fluid-filled pipettes to sample the cytoplasm of a rat spinal cord neuron.
B) electrodes located on either side of the cell membrane of the squid giant axon.
C) batteries to cause electrical changes in the membrane potential of sensory neurons.
D) patch clamps to determine the activity of individual ion channels in brain neurons.
E) recording pipettes to measure the activity of ion channels in the giant axons of earthworms.