@qihua-william are you sure you are reading the question right ? Or what exactly are your options for answers ?
If this were a true/false question, I would have to say that statement is false.
The reasoning is shown in this section of the reading (and in the video corresponding):
So basically if the source letter and the target letter are the same… There is nothing to replace. This you’d have no cost.
But as mentioned, this statement is false, so it is actually the other way around. I.e. "The value
D[i−1,j−1]+rep_cost is valid only when the source letter is different from the target letter, otherwise, the last value would be D[i−1,j−1].”