For Q20, read this: http://en.wikipedia.org/wiki/Standard_error_(statistics)
Regarding (iii):
1. Read this (well I think it's funny and it's something I didn't know): Urban Dictionary: grauniad
2. Read this regarding iii (c): Poisson distribution
3. Read this regarding iii (a): Poisson process - Wikipedia, the free encyclopedia
Now read this: Poisson distribution - Wikipedia, the free encyclopedia
So which option does that leave ....?