[单选题]
How many water moleculexwgc,h.vn7 w+07hrq/ay4ng x a4ux+fp 4w4nmu7z7 4 rtr7kjjs are there in 36 g of water? Express your answer as a multiple of Avogadro's n7n7xtr 4pk ur4zwu aj4f7m+j 4umber NA. (The molecular structure of a water molecule is $H_2 O$.)
A. $36 \; NA$
B. $2 \; NA$
C. $18 \; NA$
D. none of the above
