simple present relative clauses (in definitions) should/must/have to adverbs of frequency would/should simple present sequence markers suggest + subj. present simple passive be rich in/high in attributive clauses (which, that) as ... as but/while/whereas adverbials of time sequence markers past simple past perfect 3rd conditional past continuous must/may/might have present simple imperatives it hurts when sequence markers future simple/continuous percentages/proportions/fractions numbers and figures present perfect present continuous future simple going to modals formal letter format passive voice cause/effect indirect questions (I dont know why ... ,etc.)