Which of the following topics would lend itself only to a formal style writing folk songs you have sung psychological effects nuclear weapons how lost 10 pounds why living in country is?

The topic that would lend itself only to a formal style of writing is psychological effects of nuclear weapons.

Here's why:

* Folk songs are often about personal experiences, emotions, and everyday life. The other topics (folk songs you have sung, how you lost 10 pounds, why you like living in the country) fit into this category.

* Nuclear weapons are a serious and complex issue with significant political and scientific implications. A formal style is needed to discuss the topic responsibly and accurately.

While folk songs can touch on serious topics, they generally use a more informal and personal approach. A song about the psychological effects of nuclear weapons would likely be more effective and impactful if written in a formal and analytical way.