What is the mode of the following sequence of letter grades: {A,B,B,C,A,B,D}\{\text{A}, \text{B}, \text{B}, \text{C}, \text{A}, \text{B}, \text{D}\}{A,B,B,C,A,B,D}?
A\text{A}A
B\text{B}B
C\text{C}C
There is no mode.