The equation ________ cannot be further simplified.

• A. <img src="/_files/images/digital-electronics/digital-systems/fba4_1016a1.gif" align="center">
• B. <img src="/_files/images/digital-electronics/digital-systems/fba4_1016b1.gif" align="center">
• C. <img src="/_files/images/digital-electronics/digital-systems/fba4_1016c1.gif" align="center">
• D. <img src="/_files/images/digital-electronics/digital-systems/fba4_1016d1.gif" align="center">