Answer: Due to
Step-by-step explanation:
First, getting rid of the automatically wrong answers, finally, and as a result. (As a result shows the EFFECT, and finally doesn't show anything in a cause)
And if you put verbs in front of the rest of the responses, you can see therefore shows an effect-ish sentence while due to doesn't.
EXAMPLE: Due to the explosion, the workers cannot able to work again after a while.
Sorry if this was a little bit wordy, but hope this helps!