Why use "all of the flowers" instead of "all the flowers"?

English as a Second Language English Teacher Explanations (ESL Tests)
1

English Grammar Tests, Elementary Level

ESL/EFL Test #276 [color=blue]“Basic Grammar Exercises (6)”, question 6

I like … of the flowers in this bouquet.

(a) every
(b) together
(c) sum
(d) all

English Grammar Tests, Elementary Level

ESL/EFL Test #276 [color=blue]“Basic Grammar Exercises (6)”, answer 6

I like all of the flowers in this bouquet.

Correct answer: (d) all

Your answer was: [color=red]incorrect
I like every of the flowers in this bouquet.
[size=200]_________________________[/size]

Dear teachers,
Why use “all of the flowers” instead of “all the flowers”?

Thx

2

Both are fine. ‘Of’ is optional there.

3

Why is it wrong to say “I like every of the flowers”? I mean, every and all are not synonims?

4

You seem to have answered your own question. They are not synonyms so you cannot use one in place of the other.

‘all’ is appropriate in the example sentence.
To use ‘every’ you would have to say
‘I like every one of the flowers in the bouquet’.

You could also say ‘I like each one of the flowers in the bouquet.’