汽油机燃料供给系的作用是根据发动机各种不同工况的要求，将洁净的汽油或汽油和空气配制出适当浓度的混合气，按一定的时间和数量供入( )。

(), the number of private cars will increase sharply in...

单项选择题(), the number of private cars will increase sharply in the coming couple of years.
A. Undoubtedly
B. Doubtedly
C. Undoubted

We can certainly deliver high-quality education to many...

单项选择题We can certainly deliver high-quality education to many students at much()cost.
A. low
B. lowest
C. lower

Keeping eye contact makes the other person()welcome and...

单项选择题Keeping eye contact makes the other person()welcome and comfortable.
A. feel
B. to feel
C. feeling