Answer:
the correct anwer is option d) "Robert wanted a new car; however, he couldn´t afford to buy one.
Step-by-step explanation:
Sentence D is correctly punctuated since it is used as a conjunctive adverb. In the example provided, "however" is joining two independant sentences in order to create a compound sentence.
The correct punctuation is using "however" after a semicolon and before a comma.
The rest of the options do not follow the punctuation rule mentioned before.