_______ eager to get access to the president, the boy in northern America wrote a letter to him.

When asked why he prefers bikes to buses, the professor said,  “Riding a bicycle takes __________ half an hour, but it’s more convenient and environmentally friendly. ”

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

As is known to all language learners, the newly learnt words will soon be forgotten unless ______ used in everyday communication.

The monitor said that the learning method he used         improved his maths.