C). nitrate ion in the digestive tract d) potassium ion in the digestive tract. 35. normally a water considered soft that contains a). 0-60 mg/l of caco3 equivalent b). 61-12 mg/l of caco3 equivalent c). 121-180 mg/l of caco3 equivalent d). > 180 mg/l of caco3 equivalent e). none of the above 36. unpolluted fresh waters usually have a ph between a). 4,0-9.0 b). 2.0-4.0 c). 7.0-10.0 d). 10-14 e). none of the above 37. the phosphorus level in domestic water supply should be a). 1 mg/l b). below 1 mg/l c). above 2 mg/l d). below 2 mg/l e). none of the above 38. which of the following is an intestinal protozoan? a). rhizobium b). nitrosomonas c). cryptosporidium d). diatom e). none of the above 39. the maximum contamination levels (mcls) for public drinking water supplies in the u. s. for chemical such as carbon tetrachloride is a), 0.5 ㎍/1. c). 15ug/1, d). 2.0 pg/l, e). none of the above