choose
He is the most intellegent boy (who -that ) Ihave ever seen
He is the only man (who -That )won the prize
ارجو التوضيح ولكم الشكر

بعد صفات التفضيل و only نستخدم that

بعد صفات التفضيل و only نستخدم that
جزاكم الله خيرا

لأ خطأ لأن
He is the most intelligent boy who visited us.

Choose

He is the most intelligent boy (who-that) I have ever seen
He is the only man (who-That) won the prize
لأنها فى الجملة الاولى مفعول ولذلك يمكن استخدام that بدل who , كما يمكن حذفهما كليهما وعدم وضع اى شىء.
الا انه لا يمكن استخدامها بدل who فى حالة الفاعل كما فى الجملة الثانية وأيضا لايمكن حذفها.

The couple who live next to us have sixteen grandchildren.
Notice that we don't put a comma between the noun and a defining relative clause.

Relative clauses begin with a relative pronoun: a wh-word (who, which, etc.) or that.
However, sometimes we omit the wh-word I that and use a zero relative pronoun (see B below):

• We went to a restaurant (which/that) Jane had recommended to us.

We prefer to put a relative clause immediately after or as close as possible to the noun it adds information to:

• The building for sale was the house which had a slate roof and was by the stream.
• (rather than The building for sale was the house by the stream which had a slateroof.)
In the following sentences the relative pronoun is the object. Notice that there is a noun (or pronoun) between the relative pronoun and the verb in the relative clause. In this case, we can use a zero relative pronoun:

• He showed me the rocks (which/that) he had brought back from Australia.
• That's the man (who/that) I met at Allison's party.