Complex sentences are formed of one independent (main) clause, and one or more dependent (subordinate) clauses. The 'sequence of tenses' rule mean that verbs in the subordinate clause must be 'in agreement' with the verb in the independent clause. http://easyenglishtime.blogspot.com/2014/05/the-sequence-of-tenses.html
..by Milena Ristić
My sister is bad-tempered and would snp at anybody whenever she feels like it.