When using a two-point calibration method to correct pH on a pH meter, if the test solution is acidic, the appropriate standard buffer solution should be
选项：

A:Standard buffer solutions (25℃) at pH 6.864 and 9.182.
B:Standard buffer solution at pH 4.003 (25℃).
C:Standard buffer solutions (25℃) at pH 6.864 and 4.003.
D:Standard buffer solution at pH 6.864 (25℃).