This year I have been teaching introductory geology laboratories.
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It's been really challenging, but it's been fun working with students.
( ( ( ( ( It ( 's ( been ( really challenging ) ) ) ) , ) but ) ( it ( 's ( been ( fun ( working ( with students ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP It)) (VP (VBZ 's) (VP (VBN been) (ADJP (RB really) (JJ challenging))))) (, ,) (CC but) (S (NP (PRP it)) (VP (VBZ 's) (VP (VBN been) (NP (NP (NN fun)) (VP (VBG working) (PP (IN with) (NP (NNS students)))))))) (. .)))