Easy one .........mammal bones

[angel99]

E it seems.

[kikipooh]

E is correct based on the above explanation

[hjafferi]

IMO E too.

[chilledlife]

same confusion between clue to determine v/s clue for determining.
E seems most clear in the sentence construction because in C & D it is not very clear what 'they' stands for - ie is it the mammals or is it the 'islands'

My solution is E.