you,主语
can make use of,谓语
the differences,宾语
to tell which country the foreiners of your block are from,不定式作宾语补足语
which country the foreiners of your block are from,是tell的宾语从句
which country,是从句中的介词from的宾语
the foreiners,是从句的主语
of your block,是从句中主语的定语
are,是从句的谓语
from which country,合起来作从句中的表语
全句翻译：你能根据住在你小区里的外国人的不同点来判断他们从哪里来.