If the doctor is ______ this afternoon, I will take my little daughter to him for a thorough checkup.
Great attention must be paid ______ welfare, especially in the poor area.
At this time tomorrow ______ over the Atlantic.
Chen Xiexia is the first Chinese athlete ______ the gold medal in the Beijing Olympic Games.
______ many times, he finally understood it.
Going on a trip into ______ space must be quite ______ exciting experience.