Why was 2017 Election Turnout so High?

Thinking more about the General Election result, one of its striking results (along with the return of two party politics in most of the UK) is the relatively high turnout of 68.7%.  This is the highest turnout since Tony Blair's great victory in 1997. 

One might ask how it happened.

I can think of three possible scenarios.

(a) The first is a sea change in voter attitudes.  It is arguable that the EU referendum gave a graphic demonstration to people that voting really mattered.  You went to bed apparently securely in the EU, and woke up the next morning to a crowing Nigel Farage declaring that Brexit was now irreversible.  That is certainly a stark answer to the many people I have met who feel that voting does not change anything.  Perhaps the EU referendum was a watershed moment in the same way that the Tories reputation for economic competence was broken in 1992, or the Iraq War permanently damaged Labour's reputation in 2003.
(b) It could be a change in campaign techniques.  Labour staffers are certainly claiming that 2017 saw some game changing innovations which had the effect of raising Labour turnout.  The main weakness of this argument is that the Tory turnout also rose.  The main argument in favour is that younger voters who are generally seen as most engaged in the online world, and least engaged with "traditional" techniques, saw their turnout go up by 21%
(c) Both the main Party Leaders are "marmite" politicians.  Theresa May was seen by some of her supporters as unassailable but also by others as robotic, locked into a hard Brexit strategy, wedded to a failed austerity project and so on.  Jeremy Corbyn attracts devotion among a section of the election, but his appeal is literally incomprehensible to others.  Perhaps the combination of devotion in some and repugnance in others combined to push up turnout.