A. 'Makguksu' is a kind of noodle.
B. Makguksu means noodle that crumbled and eaten carelessly, which is made from buckwheat.
Well, I believe a verb is missing between 'that' and 'crumbled'.
b. Makguksu means noodle that IS crumbed and eaten carelessly, which is made from buckwheat.
the whole sentence needs work
c. This is similar TO Ramyun, but the noodle is better cut and its texture is softer.
note the edit
alternatively : This is similar to Ramyn but the noodle is better cut and has a softer texture.
D. I think it is the most delicious.
The article 'the' lets you expect to see a noun later,
so you should either add a noun or cross out 'the'.
d1. I think it is most delicious. OR
d2. I think it is the most delicious food.