Tom often goes to school on foot,________when it rains.
About 270 million people in rural areas in China have no __________ to safe drinking water.
The flu is believed __________ by viruses that like to reproduce in the cells inside the human nose and throat.
There were violent winds of 120 kilometers per hour or more in a hurricane,__________ huge waves, heavy rain and floods.
If city noises __________ from increasing, people __________ shout to be heard even at the dinner table in 20 years from now.
We have kept in __________ touch with each other for two years and he always gives me good advice on __________ phone.