Hello everybody!

Can sbody tell me the differences between: at a certain time
and by a certain time?

Pls, i have to explain it to tho class tomorrow!

3 answers

"at a certain time" = at one specific time, such as 1:00 p.m., October 13, 2009

"by a certain time" = any time between now and some named time. Another way to say this is at or before 1:00 p.m., October 13, 2009.
Hy!
i almost forgot it! i have to write 2 or 3 example sentences as well. can sbody explain me the meanings of these two a littlebit more detailed?

thx
I don't know how much more detail you want!!

You can look up each term here, though, and you may find more ideas:

http://www.answers.com