If a membrane protein in an animal cell is involved in the cotransport of glucose and sodium ions into the cell, which of the following is most likely true?

a) the sodium ions are moving down their electrochemical gradient while glucose is moving up.
b) glucose is entering the cell along its concentration gradient.

c) sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.
d) potassium ions move across the same gradient as sodium ions.
e) a substance that blocked sodium ions from binding to the cotransport protein would also block the transport of glucose.