It really depends on what two sentences you’re writing. If you’re writing two sentences that are in contrast, you would use “however,” but if the sentences are linked together, you would use “because.” “Immediately” isn’t a common transitional device, and you would generally use “in addition” for connection between two sentences, rather than merging them into one. The best answers would be either A or B, but since we don’t have the sentences, I can’t help you there.
