for free的音標是[f??(r) fre?]，意思是免費。記憶技巧是：for表示“為了”，free表示“免費的”，合在一起就是“為了自由（免費用）”的意思。

以下是我為您列舉的英文詞源、變化形式和相關單詞，以及不少于100字的解釋：

1. "for" - 這個詞來自拉丁語"ad"，意為"到，向"，"for free"就是"免費地"的意思。

變化形式："free"本身是形容詞和副詞，表示"免費的，自由地"。

相關單詞：

"freedom" - 自由，源自拉丁語"liberty"，意為"無約束"。

"freelance" - 自由職業者，源自拉丁語"liber"，意為"自由的"。

"frequent" - 頻繁的，源自拉丁語"frequens"，意為"經常發生的"。

"freeze" - 凍結，來自古英語"frecan"，意為"凝固"。

"freight" - 貨物，來自古英語"frec"，意為“裝載”。

"freewheel" - 空轉，自由行駛，來自古英語"frecwealh"，意為“自由旋轉”。

"freely" - 自由地，無拘無束地，來自拉丁語和古英語的形容詞形式。

"freeride" - 自由騎行，來自英語單詞“free”和“ride”，表示自由騎乘。

"freewill" - 自愿的，來自拉丁語“liberty”，表示自由意志。

以上這些單詞都與“free”這個詞源有關，表示免費、自由、頻繁、自由行動、自由選擇等含義。這些單詞在英語中廣泛應用，反映了英語詞匯的豐富性和多樣性。

常用短語：

1. for free 免費

例句：You can download this software for free from our website.

2. in for it 自找倒霉

例句：He knew he was in for it when he agreed to do the job.

3. for all 無論如何

例句：For all his efforts, he still failed to win the competition.

4. in for a rough time 將要遭受艱難的處境

例句：He knew he was in for a rough time when he took on the job.

5. for all that 盡管如此

例句：For all that, she still managed to finish the race.

6. in for it 自找麻煩

例句：He knew he was in for it when he agreed to help them.

7. for good 永久地

例句：They decided to get married for good.

英文小作文：

I am a passionate person who loves to explore new things and try new experiences. One of my favorite ways to do this is by traveling. However, traveling can be expensive, especially if you want to go somewhere exotic or far away. Fortunately, there are many places that you can go for free or at a very low cost. One of my favorite places is the local park. It"s a great way to get some fresh air, exercise, and meet new people. I also enjoy volunteering at local organizations or charities because it"s a great way to give back to the community and make new friends. In conclusion, there are many ways to explore the world without spending a lot of money. It"s important to be open-minded and adventurous, and take advantage of these opportunities whenever they arise.