Complex sentence: Mostyn Thomas born in Blaina Monmouthshire in 1896, was a British baritone in the first haf of the 20th century, at the age of 13 he went to work underground in the colliery.
Split into simpler sentences: Mostyn Thomas born in Blaina Monmouthshire in 1896, was a British baritone in the first half of the 20th century. At the age of 13 he went to work underground in the colliery.