1.不仅 & 不但 

When used as a conjunction, “不仅” and “不但” always can be exchanged. For example:

- 不仅我喜欢唱歌，我妈妈也喜欢唱歌。

-不但我喜欢唱歌，我妈妈也喜欢唱歌。

Not only I but my mother also likes singing.

-他不仅会说英语，还会说法语。

-他不但会说英语，还会说法语。

He can speak not only English but also French. 

But 不仅 can also be used as an adverb. In this situation, 不仅 can not be exchanged with 不但, but it can be exchanged with 不止. For example:

- 认为他不对的不仅我一个人。= 认为他不对的不止我一个人。

I’m not the only one who thinks he is wrong.

- 这不仅是我个人的意见。= 这不止是我个人的意见。

It's not just my own opinion.

2.刚 & 刚才 & 刚刚

 If you really confound with “刚” and “刚才”, then you can use “刚刚”. 刚刚 can be used as an adverb, which means just. It can also be used as a noun, which means just now. For example:

- 他刚才在房间里看电视。= 他刚刚在房间里看电视。

He was watching TV in the room just now.

- 他刚来中国的时候不会说汉语。= 他刚刚来中国的时候不会说汉语。

When he first came to China, he couldn't speak Chinese.

3. 中国的情人节 Chinese Valentine's Day

你知道吗？中国有三个“情人节”。第一个和西方的情人节一样，在2月14号。第二个在5月20号，因为用汉语读“520”这三个数字听起来像“我爱你”。因为用“520”代表“我爱你”的做法是从网络上开始流传的，所以每年的5月20号被认为是“网络情人节”。很多人会选择在这一天结婚，庆祝。第三个情人节也叫“七夕”，在每年农历的七月初七。“七夕”来源于牛郎和织女的爱情故事，是中国传统节日中最具浪漫色彩的节日，所以它也被认为是“中国的情人节”。

Did you know that China has three "Valentine's Days"? The first one is the same as the Western Valentine's Day on February 14th. The second one is on May 20^th (that is 5/20), because the numbers "520" in Chinese sound like "I love you". The online phenomenon of using "520" to represent "I love you" started to spread online, so May 20th is known as "Internet Valentine's Day". Many people choose to get married and celebrate it on this day. The third Valentine's Day is also called "Qixi", which falls on the seventh day of the seventh lunar month every year. "Qixi" originates from the love story of Niulang and Zhinü, which is the most romantic one in Chinese traditional festivals, so it is also considered "Chinese Valentine's Day".