Reword to avoid a/an where pronunciation is unclear

src/ch12-02-reading-a-file.md

@@ -30,7 +30,8 @@ First we bring in a relevant part of the standard library with a `use`
 statement: we need `std::fs` to handle files.
 
 In `main`, the new statement `fs::read_to_string` takes the `file_path`, opens
-that file, and returns a `std::io::Result<String>` of the file’s contents.
+that file, and returns a value of type `std::io::Result<String>` that contains
+the file’s contents.
 
 After that, we again add a temporary `println!` statement that prints the value
 of `contents` after the file is read, so we can check that the program is

src/ch12-03-improving-error-handling-and-modularity.md

@@ -270,7 +270,7 @@ well, which we’ll do in the next listing.
 </Listing>
 
 Our `build` function returns a `Result` with a `Config` instance in the success
-case and a `&'static str` in the error case. Our error values will always be
+case and a string literal in the error case. Our error values will always be
 string literals that have the `'static` lifetime.
 
 We’ve made two changes in the body of the function: instead of calling `panic!`