Only a certain number are available and you have to make seat reservations for these.

只有少数车次的车票可以使用，而且你必须提前预订。

Only a certain number are available and you have to make seat reservation for these.

只有少数车次的车票可以使用，而且你必须提前预订。

Customers are advised to make seat reservations well in advance.

【reservation】建议顾客提前订座。