单项选择题
Once he set his mind to（）something, he would not give up easily.
A．do B．doing C．be doing D．having done
单项选择题 By（）your work environment and personal practices, you may be able to reduce fatigue and discomfort.
单项选择题 The commercial purpose of a trade mark is（）the goods or services of a company from those of competitors.
单项选择题 Were it not for your help, I（）in trouble now.
