Translation:This spinach and water spinach is delicious.
Spinach is not countable -- I think it should just be "this spinach," for whatever amount of spinach that is.
Yes, spinach (and water spinach) are mass nouns, like 'cheese', or 'rice'. Has to be 'This', not 'These'.
There are two separate vegetables being referred to so the English must be "This spinach and water spinach ARE delicious." Just insert other nouns and it'll be clear, e.g., "This apple and cake is delicious" is plainly wrong. What's frustrating is you have to write the incorrect English to get through the lesson.
I agree with volumniax. Also I've never heard of water spinach but I have heard kale translated as kangkung so I think that you should accept: "This spinach and kale is delicious."
The only place I am able to find "kangkung" translated as "kale" is Google Translate, and I would not consider that an authoritative source. When googling the word "kangkung" I came up with many sites in English or Indonesian (depending on which language results I ask for) for an edible plant known scientifically as ipomoea aquatica and is sometimes called "water cabbage" and a host of other vague names in English as well. Note that the English language Wikipedia entry for ipomoea aquatica say this about names in English:
Occasionally, it has also been mistakenly called "kale" in English, although kale is a variety of cabbage and is completely unrelated to water spinach, which is a species of morning glory.
This vegetable appears widely known in many Asian countries but isn't quite as known in the West (I have only heard to called either water spinach or Chinese cabbage here in the Southwest US, which is another likewise confusing moniker), although it is considered an invasive species in some US states.
But as it is not at all related to the family of vegetables that include kale and cabbage with which Westerners are familiar, I don't think broadening the acceptable answers to include "kale" is helpful here, as it could be misleading, if not actually incorrect. Preferably people should learn what Indonesians themselves mean by "kangkung" and I guess "water spinach" will have to do.
I've also heard kale translated as such, but im fairly sure they are different vegetables.
I've eaten water spinach in Indonesia and it truly is enak... But I think it's local to the region. Can't find it anywhere in the US.
Also, "the spinach and water spinach is tasty" was marked wrong.
The subject is plural (two separate nouns) so the verb should be ARE not IS