студенты тратят много времени на подготовку к обязательным предметам, которые им не нужны, из-за этого у них остается очень мало времени для действительно важных предметов
students spend a lot of time preparing for the compulsory subjects that they don't need, because of this they have very little time for the really important items
students spend a lot of time to prepare for the compulsory subjects, they do not need, because of this, they have very little time for the really important things