@bodangles
from your reference http://dictionary.cambridge.org/us/grammar/british-grammar/relative-clauses-referring-to-a-whole-sentence
" We often use these clauses in informal speaking to express an opinion or evaluation"
The SAT is not a test of informal spoken English. Of course we use “which” in informal spoken English to refer to a whole clause, even though this is not acceptable in formal writing. This is exactly why this error is put on the WRITING section of the SAT. You need a grammar reference for FORMAL WRITTEN American English for the SAT. You have to be careful about online sources that do not clearly distinguish between informal and formal usage.