What made the Twin Towers come down? After the Twin Towers had collapsed, engineers tried to find out what could have made a difference.
Gap-fill exercise
Complete the if-clauses: might/would/could (not) + have + past participle.
support the buildings better
If the steel columns had been stronger, they
.
be less heat
If there hadn't been so much jet fuel, there
.
floors not crash down
If there had been less heat,
.
more people escape
If the stairways hadn't all been in the centre of the buildings,
.
cannot crash through them
If the walls had been thicker, the planes
through them.
Check
Hint
OK