having a dinner or having dinn

Grammar一般係check唔到object的用法對錯的，因為係按句子和情況決定，唔係按文法規則決定。

只寫出個正確寫法並略解：
She is having dinner.這個dinner本身已經是一種飯餐的名詞，另外breakfast/lunch/brunch/tea/supper/late-night-snack等都一樣，不用加上article(a,an,the)已經完整。但是如果當你手多，加了一個形容詞，例如：candle-light dinner, buffet dinner, late lunch, hearty breakfast.咁就要加a了。因為你所形容是暗地裏指明跟某一頓餐。

She is having eggs.一般指炒蛋(因為炒埋都當唔止一隻)，跟上一樣，如果你手多加上「太陽蛋」，咁就要指明多少隻egg嘞。

She is having vetegables.
或
She hates (to eat) vetegables.
理由都差不多。另外fruits亦一樣，當你是綜合地表達疏菜和水果是指所有時，基本都用眾數。只有當你不是把蔬菜和水果跟種類(各種)或量詞(所有)時，才會用uncountable.
After the accident, he is in a vetegable state.(植物人這狀態)

She is having dinner. - correct
She is having a dinner party. - correct, as an adjective
She is having a dinner. - incorrect
Dinner is an uncountable noun.

She is having an egg or she is having eggs. - correct
She is having egg. - incorrect.
Egg is a countable noun.

She is having vegetables. - correct
Vegetable is a countable noun.

having a dinner or having dinnShe is having having dinner.= dinner is uncountable noun so no article of A is required.

She is having an egg . Egg is countable noun so it is correct to have an egg.

She is having some vegetable. vegetable is also uncountable noun but we need to show amount so add some