Answer:
1.
Wir machen eine Radtour durch den Wald, der nicht weit vom Dorf entfernt ist.
2.
Die Wiese, auf der die Schafe weiden, liegt hinter den Feldern.
3.
Der See, den wir im Urlaub besucht haben, liegt hinter dem Hügel.
Explanation:
First of all I want to make clear that I´m not good at explaining things at all, but I´m gonna try.
So you got to know the genus (feminine/masculine/neuter) of the noun that occurs in both sentences really well. If you do so, then it´s not so difficult at all. Because you just have to form the relative pronoun correctly after the genus. for example in point number one, "Wald" is the noun by what we can connect the sentence. "Wald" is a masculine word, so the relative pronoun is "der"
Hope I could help,
Have a nice Day ;)
