$\text{A}$ is false because we can not cancel any arbitrary number.
$\text{B}$ is true as shown below.
$0^3\;\equiv \; 0 \ (\mod \; 7)$
$1^3\;\equiv \; 1 \; (\mod \; 7)$
$2^3\;\equiv \; 1 \; (\mod \; 7)$
$3^3\;\equiv \; -1 \; (\mod \; 7)$
$4^3\;\equiv \; 1 \; (\mod \; 7)$
$5^3\;\equiv \; -1 \; (\mod \; 7)$
$6^3\;\equiv \; -1 \; (\mod \; 7)$
If we take values greater than $7$, it will lead to one of the above values.
For example $- 83\equiv 13 \equiv 1 \; \mod \; 7 \text{ or } 93 \equiv 23 \equiv 1 \; \mod \;7$