The maths problem remained confusing to the boy although __________ over and over.
| A．explaining | B．being explained | C．explained | D．having explained |
The demand that the law on gun ownership _____ be changed ___ is very strong.
| A．changes | B．will be changed | C．be changed | D．be changing |
The increase of the number of the students makes the limited computers not ________ to each student.
| A．available | B．helpful | C．acceptable | D．affordable |
He had just sent an email to his pal on the Internet ________ the system broke down.
| A．while | B．when | C．after | D．since |
While intelligent people can often ______ the complex, a fool is more likely to complicate the simple.
| A．sacrifice | B．substitute | C．simplify | D．survive |
People develop ________ preference for a particular style of learning at ________ early age and these preferences affect learning.
| A．a；an | B．a；不填 | C．不填； the | D．the；an |