Walking alone in the dark，the boy whistled to ________ his courage.

If you live in the country or have ever visited there, ______ are that you have heard birds singing to welcome the new day.

Nokia has    a family     of low-cost mobile phones based on Google's Android operating system.

Emergency line operators must always ________ calm and make sure that they get all the information they need to send help.

 More consumers are waiting for the further drop of housing prices with money in their hands _______ buying houses, according to a report.