1. It's been a few days since I changed my mac, and I feel that the screen is still too small when I use it in the company. So an external dell monitor. Only two resolutions were found. Especially unclear. Finally found a workaround on github.
Open Display Preferences. Choose default first. Then press the option to select the zoom and the highest resolution will come out.
http://sandomingo.github.io/blog/2014/04/16/macbookpro-external-display-resolution-problem/