Though he was disabled, he was never satisfied ______ he did the best of a normal child.
While we are developing agriculture and industry, we must prevent the earth ______.
When _______ help, one often says “Thank you.” or “It is kind of you “
Frank insisted that he was not asleep______ I had great difficulty in waking him up.
_______seems to have been a strong competition in China for school leavers to enter college or university.
It is these poisonous products ______can cause the symptom of the flu, such as the headache and aching muscles.