To solve this question, we need to identify which of the given websites are known for providing plagiarism checking services.

1. Option (a) http://go.turnitin.com: Turnitin is a well-known service used by educational institutions to detect plagiarism among academic works. It compares submitted papers to an extensive database of content, which includes multiple sources like academic journals, Internet content, and previously submitted papers.
   Conclusion: This is a plagiarism checking website.
2. Option (b) http://www.researhcgate.com: ResearchGate is a social networking site for scientists and researchers to share papers, ask and answer questions, and find collaborators. It does not offer plagiarism checking services.
   Conclusion: This is not a plagiarism checking website.
3. Option (c) http://www.editorial.elsevier.com: This site is associated with Elsevier, a major academic publisher. While Elsevier offers many editorial services, it is not specifically known for providing a dedicated plagiarism checking service for general use.
   Conclusion: This is not specifically a plagiarism checking website.
4. Option (d) http://www.grammarly.com: Grammarly is an online platform commonly known for grammar and spell checking. However, it also includes a plagiarism detection tool as part of its premium services, which checks written content against billions of web pages.
   Conclusion: This is a plagiarism checking website.

Based on this assessment, options (a) and (d) are the websites that provide plagiarism checking services. Therefore, the correct answer is:

(a) and (d)