Connect the units
Natural wonders of the world
Report a yes/no question with asked + if/whether + subject + verb, using statement order. “Is the path open?” → She asked if the path was open. In a past reporting context, backshift present to past and can to could; change pronouns/time expressions when the context requires it. Do not keep do/does/did or invert the subject.
Tourism
Relative pronouns connect a noun with identifying information: who for people, which for things, whose for possession. In a defining clause, that can often replace who/which. The pronoun can be omitted only when it is the object, not when it is the subject: the guide (who) we met; the guide who helped us.
World Englishes
A defining relative clause gives essential information identifying a person or thing: Students who practise regularly often gain confidence. Do not put commas around it. Who/that can refer to people and which/that to things. Only an object relative pronoun can be omitted.