struggle to do sth.

do one’s utmost to do sth.

15. 一系列

a series of

a range of

a string of

16. 毫无疑问，众所周知

undoubtedly

There is no doubt that

without doubt

No one can deny that

It is commonly acknowledged that

It goes without saying that

It is generally/ widely believed/ held/ agreed that 17.事实上

in fact

actually

as a matter of fact

practically

virtually

18. 为了

for the sake of

on behalf of

19. 有时

sometimes

at times

from time to time

on occasion

now and then

now and again

20. 越来越：

be increasingly + adj.,