However in writing, it would not be “La vie, c’est dure’ - it would be “La vie, c’est dur. “

You would still need to change/agree the adjectives etc in a written exercise, so this would not work so easily in fixed fill-in-blank questions. 

Sylvie’s example was using ‘le chômage’ so there was no issue with adjectival agreement, but in writing a comma will be placed after the first 'subject' (before ‘c’est…’), as you have done and as Cécile indicated in her response to Sylvie.

The freeform exercises allow you to practice writing French ‘as it is spoke’ as for many of them you self-mark and can accept your own answers, regardless of the bot’s suggestions and comments.