The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

if someone wanted to use Sheldon
as their sperm DONOR?
The Big Bang Theory Season 12, Episode 12

I will find an appropriate sperm DONOR
for your eggs...
The Big Bang Theory Season 1, Episode 15