When they entered the area, the visitors ____ to turn off their smartphones.
A: are requiring
B: were being required
C: were required
D: requires
A: are requiring
B: were being required
C: were required
D: requires
举一反三
- When they entered the area, the visitors (require) _________ to turn off their smartphones.
- When<br/>they entered the area, the visitors ______ to turn off their<br/>smartphones. (require)
- When they entered the area, the visitors ( require) to turn off their smartphones. The answer isisrequired.
- 201712A Structure B Directions: Fill in the blank with the proper form of the word given in bracket. When they entered the area, the visitors (require) ____________ to turn off their smartphones.
- The research scientists often meet with problems_____new types of instrument for their solution. A: requiring B: required C: to require D: being required