A. document.getElementById("tb").cells[2][1].style.background-color='#ff0000'; B. document.getElementById("tb").rows[2].cells[1].style.background-color='#ff0000'; C. document.getElementById("tb").rows[2].cells[1].style.backgroundColor='#ff0000'; D. document.getElementById("tb").cells[2][1].style.backgroundColor='#ff0000';