A Membrane Potential Is Plotted Over Time in the Following

Multiple Choice

A membrane potential is plotted over time in the following graph. The Nernst equilibrium potentials for four ions (A to D) that affect the membrane potential in this system are indicated in the graph. What happened in the time period indicated by a question mark?

A) Channels conducting ion A opened.
B) Channels conducting ion B opened.
C) Channels conducting ion C opened.
D) Channels conducting ion D opened.
E) Channels conducting ion A and C opened.