Complex sentence: U-shaped development can be seen in cognitive skills such as learning new words, or doing high level algorithms in mathematics the skill can also be artistic such as painting or playing a musical instrument, and physical skills such a walking and weight lifting.
Split into simpler sentences: U-shaped development can be seen in cognitive skills such as learning new words, or doing high level algorithms in mathematics. The skill can also be artistic such as painting or playing a musical instrument, and physical skills such a walking and weight lifting.