Complex sentence: The first, "Tintin in the Indies", appeared at Brussels'Theatre des Galeries in April 1941, while the second, "Mr Boullock's Disappearance", was performed there in December.
Split into simpler sentences: The first, "Tintin in the Indies", appeared at the Theatre des Galeries in April 1941. The second, "Mr Boullock's Disappearance", was performed there in December.