单项选择题
For any numbers a, b, and c,
For which of the following equations is it true that there is exactly one positive integer that satisfies it' （）
A. none
B. Ⅰ only
C. Ⅲ only
D. Ⅰ and Ⅲ only
E. Ⅰ, Ⅱ, and Ⅲ
单项选择题
For any numbers a, b, and c, For which of the following equations is it true that there is exactly one positive integer that satisfies it' （）
A. none
B. Ⅰ only
C. Ⅲ only
D. Ⅰ and Ⅲ only
E. Ⅰ, Ⅱ, and Ⅲ