In the given question, a sentence is given with a part of it missing and represented by a blank. Choose the phrase that can be placed in the given blank to make a meaningful and grammatically correct sentence.
When a certain temperature threshold is crossed, suddenly a large proportion of species face conditions __________, and the ecosystem can abruptly collapse.
1
they are used to
2
they have not experienced before
3
they can enjoy
4
which may help them to increase in number
5
None of these