Mrs. Brown helps me out when I have too much work to do, and I return her _______whenever I can.
Air is________and of no smell but we can feel its motion when there is a wind.
Mountain climbing must be very tiring, ________,you might feel sick with the air getting thinner.
Mark’s fluency in English gave him a big advantage________the other applicants for the job.
In China, as we all know, brides are often dressed in red as it is a________of good fortune.
________number of people who own luxury cars is on ________increase every year.