In the "Preparing for Data Import" topic we are taught to "Clean up the import file for accuracy and consistency. This involves updating the data to remove duplicates..."
In the import file for the challenge though there is an obvious duplicate John Dodge and Jack Dodge with the same mobile number. (Jack is a common diminutive / nick name for John). If you remove the duplicate though you fail the challenge. Leave the duplicate in and you pass. There also doesn't seem to be any need to remove formatting from phone numbers as shown in the video. Don't mean to be pedantic, but maybe a good idea to remove the duplicate so we don't have to spend time wondering whether to remove it or not. Or maybe in the instructions for the challenge, just say "No need to clean the data prior to importing" or something.
Cheers

Hi, I'm a newby and am wondering whether I should be starting out with Apex or Lightning? I will be developing commercial apps that integrate with the Sage Life product. So, basically doing accountng related apps mainly for desktop (ie: browser) but also for mobile phone/watch UI's.

https://developer.salesforce.com/trailhead/force_com_introduction/data_management/data_import
I've tried 5-6 times now to use import wizard to import the file provided for the Data Management Module of Force.com Basics.  It just continues to give me an "There was a problem uploading the CSV file. Try again, or choose another file."  I've tried this on both a PC and a Mac, Chrome and Firefox and browsing to the file or drag and dropping the file, just get the same error every time.