( ( Hundreds ( of ( years ( of ( ( observing ( the sunspots ) ) ( on ( the Sun ) ) ) ) ) ) ) ( ( shows ( that ( ( ( the number ) ( of sunspots ) ) ( varies ( in ( ( a cycle ) ( with ( ( an ( average period ) ) ( of ( 11 years ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNS Hundreds)) (PP (IN of) (NP (NP (NNS years)) (PP (IN of) (S (VP (VBG observing) (NP (DT the) (NNS sunspots)) (PP (IN on) (NP (DT the) (NNP Sun))))))))) (VP (VBZ shows) (SBAR (IN that) (S (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS sunspots)))) (VP (VBZ varies) (PP (IN in) (NP (NP (DT a) (NN cycle)) (PP (IN with) (NP (NP (DT an) (JJ average) (NN period)) (PP (IN of) (NP (CD 11) (NNS years))))))))))) (. .)))
Hundreds of years of observing the sunspots on the Sun shows that the number of sunspots varies in a cycle with an average period of 11 years.
(ROOT (S (NP (NNS Sunspots)) (VP (VBP occur) (PP (IN in) (NP (DT a) (CD 11) (NN year) (NN cycle)))) (. .)))