同学们首先以轻松愉快的话题引入了宣讲的主要内容。

First of all students relaxed and happy to introduce the topic of the main content of the lectures.

尿床可是个不愉快的话题。尿床困扰着500万至700万名美国儿童。

Never a happy topic, bed wetting is a very distressing problemfor five to seven million American kids.

尿床可是个不愉快的话题。尿床困扰着500万至700万名美国儿童。

Never a happy topic, bed wetting is a very distressing problem for five to seven million American kids.

交谈的内容是有关自身安全和愉快的社交的话题。

Their conversation speaks of their own safe and comfortable society.

尽管意外、疾病和死亡都是一些令人不愉快的话题，但我们应该面对它们。

Although accidents, illness and death are not unpleasure subjects. but we should look them in the face.