Read the Following Paragraphs and Answer the Questions After Each

Read the following paragraphs and answer the questions after each paragraph.
The United States has not made a mistake by admitting millions of immigrants since the law was changed in 1965. Indeed, America's liberal immigration policy is one of our proudest public accomplishments. But America's liberal immigration policy is more likely to find continued acceptance among most Americans and keep the nativists at bay if the immigration preference system is changed to assure a fairer and more nationally diverse pool of immigrants. So let's not turn our backs on one of the most successful American ideas. Let's get it right.
-Peter Salins
-What is the paragraph's topic sentence? Does Salins state his opinion about a certain issue? Is this opinion debatable?