Cleft sentences and inversion

Which is the correct one?

What he doesn't appreciate ...

• how hard can the new concepts be.

• how hard can be the new concepts.

• how hard the new concepts can be.

• how hard the new can be concepts.

Put emphasis.

"I love the photos on that website".

• That I love about that website is photos.

• What I love about that website is photos.

• What I love about that website are photos.

• Which I love about that website is photos.

Tim arrived two hours late:

• What had happened is that bicycle chain had broken.

• What happened was that bicycle chain broken.

• What has happened was that bicycle chain has broken.

• What had happened was that bicycle chain had broken.

Passengers are never permitted to open the door themselves.

• Under no circumstances are passengers permitted to open the doors themselves.

• Under no circumstances

  passengers are permitted to open the doors themselves.

• Are passengers permitted to open the doors themselves under no circumstances .

• Passengers are permitted to open the doors themselves under no circumstances .

This was the first time the race had been won by an European athlete.

• Not until had the race had been won by an European athlete.

• Never before the race had been won by an European athlete.

• Not until this time the race had been won by an European athlete.

• Never before had the race been won by an European athlete.

The telephone started ringing just after he had left the office.

• Barely he had left the office when the telephone started ringing.

• Barely did he leave the office when the telephone had started ringing.

• Barely he did leave the office when the telephone had started ringing.

• Barely had he left the office when the telephone started ringing.