Survival of the fittest. The pesticides only kill a certain number of pests. Those survived have less competition and became stronger.

It is the same. Film is a slang for movies because before digital, movies were captured onto thin plastic strips (film).

I am falling apart since the chains used to hold me together. I don't care anymore because when I did, I carried the world on my shoulders.

Both sentences are grammatically correct. When to use one or the other depends on how you, the writer, want to emphasize a time period to the reader. In the first sentence, the reader is listening to you telling a story about something that has already happened. In the second sentence, the reader is listening to you telling a story that is current and still happening.

Yes, it is correct. However, if this is at the end of a business letter, then it is preferable to use "looking forward to...". It has a stronger connotation and not passive like "hope to...".

Use Frankie Singh's response for the first part. Second part: So, do you want to learn Chinese? I am fluent in Mandarin. If you want to learn Chinese, contact me. We can learn from each other and progress together.