Could anyone help me to answer these questions Thank you very much!
Do these two sentences have the same meaning?
-He will be difficult to replace when he leave.
-It is difficult to replace him

Is "Encyclopedia's" a typo (the " 's" is wrong) or a correct word? If it's correct could you write the full form (Encyclopedia's ...)? What 's represent for?
Encyclopedia's on DVD-ROM

Could you tell me the meaning of practice in this sentence? I look it up in a dictionary and there are many meaning and I don't know which meaning is being used in this case?
A traditional and long-established practice is for children to study and gain knowledge at school.

Question

Could anyone help me to answer these questions Thank you very much!
Do these two sentences have the same meaning?
-He will be difficult to replace when he leave.
-It is difficult to replace him

Is "Encyclopedia's" a typo (the " 's" is wrong) or a correct word? If it's correct could you write the full form (Encyclopedia's ...)? What 's represent for?
Encyclopedia's on DVD-ROM

Could you tell me the meaning of practice in this sentence? I look it up in a dictionary and there are many meaning and I don't know which meaning is being used in this case?
A traditional and long-established practice is for children to study and gain knowledge at school.

Answer

-He will be difficult to replace when he leaveS.
-It is difficult to replace him

The first is talking about the future. The second suggests he has already left, although I would normally say something like "We are finding it difficult to replace him"

Encyclopedias is correct.

Practice is a way of doing something that happens regularly. A bit like tradition or habit.

It is our practice to answer all emails within one day.