15. A birthday cake whose batter is made from invasive plants will take along while to digest, but a cupcake made of frosting died with extract from the ground blossoms of red sesbanias, another invasive plant, goes down easily.

Ans: 15. A birthday cake whose batter is made from invasive plants will take a long while to digest, but a cupcake made of frosting dyed with extract from the ground blossoms of red sesbanias, another invasive plant, goes down easily.

1) "died" should be "dyed"

2) "Along" is a preposition. Here "a long" is working as a preposition for "while"