Many books are in the bookcase.

There are many English books in the bookcase.

Books are books. The plural form of book is books, the singular form of the third person is books, the past tense form is booked, the past participle form is booked, and the present participle form is booking. Bookcase means bookcase. There are many other expressions. Similar sentences are as follows:

Many seabirds died in the oil spill.

Many seabirds died because of the oil spill.

Many companies suffer from the lack of skilled staff.

Many companies suffer from a shortage of skilled staff.

Many immigrants are well educated.

Many immigrants are well educated.

This model has many new features.

This model embodies many new features.