Questions about example sentences with, and the definition and usage of "Oih"

Q: There are those who doubt of my hability to cook. soa natural?

Q: How is my hability of giving opinions in the following text? Also, how about my pronunciation? Is there anything I should improve to sound alike a native?

"The advice which concerns about expanding my answers by giving examples, reasons and explanations and additional information is the most useful, in my opinion. The reason for this is that a detailed answer has many more chance of accomplishing the examiner's pourposes."

Q: How about of my hability of giving opinions in the following text? Is there anything to fix in order to show more proficience?

"I would save the polar bears if I could, because I find them so emblematic, as they are the main representatives of the Artic fauna".