Suppose $a<c$ and $b<0$. Which of the following must be true?

$ab < ac$
$a+b<c+b$
$a-b < c-b$
$c/a > 1$

Enter your answer as a list of those options that are always true. For instance, if you think only the first and third are true, enter 'A, C'.
If we consider a negative $a$ and a positive $c$, we can see that this is not true.
If we subtract $b$ from both sides we get $a<c$ which we know is true.
Adding $b$ to both sides again gives us $a<c$ which we know is true.
Again, if we consider a negative $a$ and a positive $c$, we see that $c/a$ is negative and hence not greater than $1$.

Thus, the answer is $\boxed{B, C}$.