Some are from America,and some ____ England and Canada.

是from,我认为要加are

of 英国和加拿大的 如是from 应加are

from,不加are

答案是"of"
是from则必须之前加are
整个句子如果用with和about明显翻译不同
因为句子考察的是主要意思是”从．．．来”
故，综上所述，为"of"

C.已经有前文的提示了可以省略的.

c) from,

since it is mentioned ahead, the later sentence should omit the verb 'are'.

Hope that helps.