The correct answer is A. lty.
lty stands for line type. It is a character string that specifies the type of line to be used. The default value is 1, which is a solid line. Other possible values include 2 (dashed line), 3 (dotted line), 4 (dash-dot line), and 5 (long-dash line).
pch stands for point character. It is a character string that specifies the type of point to be used to represent data points. The default value is 1, which is a circle. Other possible values include 2 (square), 3 (triangle), 4 (diamond), 5 (x), and 6 (plus sign).
lwd stands for line width. It is a numeric value that specifies the width of the line to be used. The default value is 1.
Therefore, the only parameter that defines line type is lty.