Is English an optional lesson, or does everyone have to learn it?

英语是选修课还是必修的课程？

The goods are optional, but only one.

这些物品是可以任选的, 但只能选一。

Attendance at the lecture is optional.

这一讲座可随意参加。

Indirect cooling circuit via heat exchanger allowing optional heat recovery for the calorifier or cabin heating.

间接排气管水冷却方式，当水流经热交换器时，允许水流经任意方向通过水与废气热交换器或散热箱。

Inserts at the lower cone bottom , filter out iron mixed with raw materials , optional madel available.

放入锥斗底部，过滤掉残杂在原料中的铁质物件。有多种结构形式以供选择。

It is optional with you.

那是你的由。

Ingredients：10pc Vietnamese rice paper, 10pcs Shrimp, 50g Jicama, 50g Vermicelli, 5g Dried Wood-ear fungus, some Minced Garlic, optional amount of Sweet Basil and Coriander.

乾米纸春卷皮10张、中虾10只、沙葛50克、粉丝50克、乾木耳5克、蒜茸少许、九层塔叶及芫荽适量。