Hello,
The answer is option A pay attention to URL endings, such as .gov and .com.
Reason:
Its A because its a very important guideline to make sure you look for the root words .gov and .com to make sure its professional. Its not option B because using search engines can cause viruses. Its also not option C because anything can look professional just by how the website looks and says.
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit