It's all about matching the sentence pieces to make a sensible sentence.
2) A blue whale's heart, which can weigh over two tons, beats 8-10 beats per minute.
3) Hyperion, which is the name of a redwood in California, is the world's tallest tree.
4) The African forest elephant, which is smaller than the Savannah elephant, is also in sharper decline.
5) A male white rhino, which is about the size of a quad bike, is nearly twice as heavy as a male black rhino.
I think these are the correct answers! Hope that helps!