Complex sentence: The first Duplo bricks had 2 x 4 knobs appear in two sets in 1969 and the bricks were made in four colours red, yellow, blue and white.
Split into simpler sentences: The first Duplo bricks, which had 2 rows of 4 knobs each, appeared in two sets in 1969. The bricks were available in four colours--red, yellow, blue and white.