37, There has been a slight drop in the number of people using public transport (slightly)
=> The number of people using public transport has dropped slightly
38, Revising for exams takes up all my time at the moment (busy)
=> I'm busy revising for exams at the moment
39, There was an increased demand for travel , sothe government decided to invest in building the very first metro systems (as)
=> The government decided to invest in building the very first metro systems as there was an increased demand for travel
40, I don't know much about historical events , so I can't help her with her history homework (if)
=> If I knew about historical events, I could help her with her history homework