The research is so designed that once _____ nothing can be d

The research is so designed that once _____ nothing can be done to change it.
A begins
B having begun
C begining
D begun
_____ in thought,he almost ran into the car in front of him.
A Losing
B Having lost
C Lost
D To lose
If you go to Xi'an,you will find the palaces there more magnificent than commonly _____
A supposing
B supposed
C to suppose
D suppose
Jane and John still remember that it was _____,their parents,who encouraged them to continue the education
A whose
B who
C they
D whom
By this time next year,you _____ a vocabulary of 800 words.
A.will have
B.will have had
C.have
D.have had

1.D once后省略了it is,补充完整应该是The research is so designed that once it is _____ nothing can be done to change it.这样可以明显地看出it指代The research,与begin构成被动关系,故选D.
2.C be lost in thought 这是一个固定表达,意为“陷入沉思”.而该题中用作状语,仅保留过去分词即可.
3.B 该句意为“如果你去西安,你会发现那里的宫殿比人们通常认为的更有意义”.宫殿与suppose构成被动关系,即人认为宫殿有意义,宫殿被认为有意义.
4.C ...it was _____,their parents,who ...这是一个强调句型,强调主语,只不过被强调的部分they,their parents是一个同位语.
5.B By this time next year这一时间状语提示我们应该用将来完成式“will have done” .