Despite the abundance and importance of maize, its biological origin has been a long-running mystery. The bright yellow, mouth-watering treat does not grow in the wild anywhere on the planet, so its (i)___ is not at all (ii)___.
Something that is long-running has been in existence, or has been performed, for a long time.
...efforts to find a peaceful solution to this long-running war.
...a long-running trade dispute...
He was best-known for his role in the long-running television series.
ADJ-GRADED: ADJ n
Mouth-watering food looks or smells extremely nice.
...hundreds of cheeses, in a mouth-watering variety of shapes, textures and tastes.
...more than 150 mouthwatering recipes.
ADJ-GRADED also mouthwatering.
If you describe something as mouth-watering, you are emphasizing that it is very attractive. (JOURNALISM)
Prizes worth a mouth-watering s9.6 million are unclaimed.
ADJ-GRADED also mouthwatering. emphasis
1 a : an entertainment given without expense to those invited b : the act of providing another with free food, drink, or entertainment
2 : an especially unexpected source of joy, delight, or amusement
文中把玉米说成一种 treat，显然应该对应第二种理解，玉米给人带来快乐，为了不吓人，意译为 “ 好东西 ” 。