fix a grammar error in the classify engine comments

OTSCPP/OTSClassifyEngine/ExpressionClassifyEngine.cpp

@@ -426,7 +426,7 @@ CElementChemistriesList ExpressionClassifyEngine::ZeroElementProcess(COTSParticl
 			}
 		}
 		if (bMatch == false) continue;
-		// all the rule's using element are contained in the particle then we replace the element with the percentage value
+		// all the rule's using elements are contained in the particle then we replace the element with the percentage value
 
 		for (std::string s : rule->GetOtherpropertyList())
 		{