original: natural ytterbium is a mix of seven stable isotopes .
simplifications: natural ytterbium is a combination of seven stable isotopes . natural ytterbium is a mix of seven stable isotopes . natural ytterbium is a mix of seven stable isotopes . natural ytterbium is a mix of seven stable isotopes . natural ytterbium is a mixture of seven stable isotopes . natural ytterbium is a mix of seven stable isotopes . natural ytterbium is a mix of seven stable isotopes . ytterbium is made of seven isotopes .