<p>Following the distinction that “due to” should function as an adjective and “because of” should function as an adverb, “because of” must be used in that sentence. “because of the rain” is modifying “I cannot go,” not a noun.</p>
<p>Just so you know, this kind of thing (using “due to” or “because of”) is probably not tested on the SAT. CB knows that grammar rules (especially more obscure ones like this one) are rather finicky and have some exceptions that could lead to their being sued.</p>
<p>Still, it’s something good to know (if you can understand Silverturtle’s explanation; I really can’t seem to follow what he’s saying). You should be able to get by in life without ever understanding this rule.</p>