also用在句中(一般放在be动词和助动词之后,行为动词之前).
she also is good at English.
she also like English.
too 多用于口语,位于句未或句中,只用于肯定句,其前常有逗号.
They are students,too.=They,too,are students.
否定句为They are students,either.
as well 用于肯定句,通常位于句中或句尾.
He knows French,and he knows English as well.