一個英語句子的分析----高手幫忙

題目：

一個英語句子的分析----高手幫忙
These books have many advantages.One of them is that we can find a variety of topics,such as science,culture and history.These topics,I think,are very popular with us students.【What’s more,along with the text there are many beautiful and colorful pictures,which can help us understand English better.】 Even the students who used to dislike English have turned out to be interested in the subject.However,【some of the texts have too many new words and expressions which are hard for us.】 Therefore,I』d like to suggest changing them into easier ones.
請解釋【】里的兩個句子（爲方便解釋,我給出了這段文章的全部）
第一個What’s more,along with the text there are many beautiful and colorful pictures,which can help us understand English better.這裡爲什麼which之前要加逗號構成非限定性定語從句.
第二個some of the texts have too many new words and expressions which are hard for us.
這個句子爲什麼which之前沒有用逗號.
請對比這兩個句子,解釋什麼情況下用「限定性定語從句」,什麼情況下用「非限定性定語從句」.詳解.

解答：

第兩個句子,都可以加逗號形成非限定性定語從句,也可以不加形成限定性的,這兩個都沒錯,只是它選擇用這種說法.區別不大