Why is rye uncountable?

[Ryi]

English Language Tests, Intermediate level

ESL/EFL Test #227 "Confusing Words test (10)", question 2

There is a great deli around the corner. Tom orders corned beef on ......... bread for lunch every day.

(a) root
(b) reed
(c) wry
(d) rye

English Language Tests, Intermediate level

ESL/EFL Test #227 "Confusing Words test (10)", answer 2

There is a great deli around the corner. Tom orders corned beef on rye bread for lunch every day.

Correct answer: (d) rye
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What is a rye

[Mister Micawber]

.
'Rye' is uncountable. It is a kind of grain.
.
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Native English teacher at Mister Micawber's

[Ha Kim Yen]

Dear teachers,
Can you give me the reason why we use draft in this sentence. What does it mean here?
The window latch broke earlier in the day. By nightfall, the wind was blowing harder than ever, and there was a noticeable draft in the apartment.
Thank you so much!

[Mister Micawber]

draft = a current of air (usually coming into a room or vehicle)
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Native English teacher at Mister Micawber's