they will study at home __A___ computer.（他们将会在家通过电脑学习）
A.on B.in C.on the
on computer 通过电脑...
例句：My sister will study at school on computer.
我的妹妹将会在学校通过电脑学习.
on the computer在电脑上面
例句：My book is on the computer.
我的书本在电脑上面.
in computer（没什么意思）
例句：I have experience in computer operation.
我有电脑操作经验.