My mother is going to host a TV show on cooking. She cooks very well. (who)
The joined sentence is: My mother, who cooks very well, is going to host a TV show on cooking.
Here, the relative pronoun who connects the two sentences by providing extra information about the noun 'My mother'. Since 'My mother' is a specific person, the clause added is a non-defining relative clause. We already know her identity, so the clause does not define her but simply adds more details.
As per the rules for non-defining relative clauses, such clauses must be separated from the rest of the sentence by punctuation marks like commas or dashes. Therefore, the clause is enclosed between two commas in the final sentence.
Explanation
The textbook explains that when providing extra information about a specific person whose identity is already known, we use a non-defining relative clause beginning with 'who'. Since 'My mother' is a particular person, the clause 'who cooks very well' is non-defining and must be enclosed in commas.
Solution Steps
Step 1: Identify the subject 'My mother' and the extra information 'She cooks very well'.
Step 2: Replace 'She' with the relative pronoun 'who' to form the relative clause 'who cooks very well'.
Step 3: Since it is a non-defining relative clause providing extra information about a specific person, insert it right after 'My mother' and separate it with commas.