They were all out _________ the missingchild.

－______ does it take you to water the flowers －Thirty minutes.

________ your major, you’ll have to take general education classes in your first two years of college.[ ]

The stone on the river bank rolled under her feet； she was _____into the river，and she called out for help

he word “PM2.5” _________ appearing in media reports, people pay greater attention to it and seek health tips for smoggy days.