They ______ the train until it disappeared in the distance.

My father’s new cell phone can be used _________ e-mails. But he says he isn’t used ________ on such a small screen.

Often, when he ______ something that ______ him, he wasted his time drawing some little pictures.

The child tiptoed quietly to the bird ________ into theforest when he was about to catch it

An e-book is usually much______ than an ordinary paper book.