The correct option is
D A glass
The correct answer is Option B.
Countable nouns are those that can be measured in exact numbers.
Uncountable nouns are those that that can not be counted in exact numbers.
Since 'glass' can be counted in exact numbers, it is a countable noun.
Therefore Option B- 'a glass' is the correct answer.
The other options are incorrect because:
Option A: SOME GLASS- some is used with uncountable nouns and glass is a countable noun.
Option C: A PIECE OF GLASS- this would make an incorrect sentence. One cannot demand a piece of glass of water.
Option D: ALL GLASS also is not grammatically correct.
Hence Option B is the correct answer.