Right choice is (a) AvPI and AtNHX
The best I can explain: AvPI (Arabidopsis vacuola protein I) and AtNHX (Arabidosis transporting H^+ ion) are the antiport proteins present on the membrane of vacuole. During salt stress condition, there is an increase in Na+ ion in the cell, which leads to acidity in cell and may be harmful to plants. These antiport transport Na^+ ion into the vacuole from cytoplasm coupled with the transport of H^+ ion from vacuole to cytoplasm. This result in reduction of Na+ concentration in cytoplasm and reduction of acidity in salt-stress condition.