Answer:
The revision that corrects the punctuation error in the sentence is C. Add a comma after the word however.
Step-by-step explanation:
When "however" is placed in the middle of a sentence and it is used to indicate that something will or will not happen in spite of something previously mentioned in the conversation, we need to place it between commas. In the sentence we are analyzing here, a comma is missing after the word "however", so we must add it to make it right:
We cannot go tomorrow, however, because I must work.
We can assume that, previously, the speaker said something about wanting to go somewhere. He/she now says that, in spite of wanting to go, he/she cannot do it because of work.