( ( ( ( ( As ( ( a basis ) ( for ( understanding ( this concept ) ) ) ) ) ( , ( students know ) ) ) : ) ( ( ( almost all ) ( of ( ( the ( Earth 's ) ) water ) ) ) ( is ( present ( as ( ( salt water ) ( in ( ( the oceans ) ( which ( cover ( most ( of ( ( the ( Earth 's ) ) surface ) ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (PP (IN As) (NP (NP (DT a) (NN basis)) (PP (IN for) (S (VP (VBG understanding) (NP (DT this) (NN concept))))))) (, ,) (NP (NNS students)) (VP (VBP know))) (: :) (S (NP (NP (RB almost) (DT all)) (PP (IN of) (NP (NP (DT the) (NN Earth) (POS 's)) (NN water)))) (VP (VBZ is) (ADJP (JJ present) (PP (IN as) (NP (NP (NN salt) (NN water)) (PP (IN in) (NP (NP (DT the) (NNS oceans)) (SBAR (WHNP (WDT which)) (S (VP (VBP cover) (NP (NP (JJS most)) (PP (IN of) (NP (NP (DT the) (NN Earth) (POS 's)) (NN surface)))))))))))))) (. .)))
As a basis for understanding this concept, students know: almost all of the Earth's water is present as salt water in the oceans which cover most of the Earth's surface.
(ROOT (S (NP (NP (JJS Most)) (PP (IN of) (NP (NP (NN earth) (POS 's)) (NN water)))) (VP (VBZ is) (VP (VBN located) (PP (IN in) (NP (NNS oceans)))))))