A baby might show fear of an unfamiliar adult, _______ he is likely to smile and reach out to another infant.

The farmer had to wear heavy boots in the winter because the fields were too wet and________.

We must ______ that the experiment is controlled as rigidly as possible.

Since William had been seriously ill for several months, his parents were worried about________ to return to school full-time.

The TV station, in ________ to massive popular demand, decided to continue the soap opera(肥皂剧 ).