How to use a bag of and a packet of

How to use a bag of and a packet of

A big bag of ice a big bag of popcorn Eg.The The king was satisfied with his answer and gave the doctor a bag of gold

A bag of milk a bag of + countable or uncountable?
What's the meaning of better than,

A bag of milk
Bag: countable
Milk: uncountable
Two / some bags of milk
I wish you a happy and progressive study
Supplement:
better than ：…… Better than Well, as long as it's a comparison between the two, it's OK
If you have any questions, you can continue to ask me

There is ( )rice in the bag.A.lot B.many C.a lot D.lots of

D lots of
There is a lot of rice in the bag
Ensure accuracy~

There are a lot of books in the bookcase

What's in the bookcase? Or how many books are in the bookcase?

There is - (lot) of pots in the bag

The predicate is wrong

"There is a lot of" or "there are a lot of"“
There is a lot of
I'm a beginner of English. Why use singular is?

A lot of is the most common term in spoken and written language. It can modify both countable nouns (equivalent to many) and uncountable nouns (equivalent to much). It is usually used in affirmative sentences
There are a lot of books in the library
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There is a lot of people here at the small park
A lot of is singular or plural

there a lot of junk food in the bag
Is it is or are
Why?

Is because junk food is an uncountable noun~~

The bag of rice is (yesterday yuan)

How much is the bag of rice?

This bag is 90 yuan.That Bag is 70 yuan
This bag is ___ ___ than that one.

more cheap

This bag of rice is heavy

This bag of rice is not light enough