The CUR_PCP_PROV ID column contains the ID of a patient's primary care provider. To check if a patient has no primary care provider, you add CUR-PCP-PROV-ID = NULL to filter your query. Before adding this filter, your query was returning many results, but now it returns zero results. Which of the following is a possible reason? T ONE OF THE FOLLOWING (1 PT) A. CUR-PCP-PROV_1D = NULL always returns UNKNOWN. B. CUR PCP PROV ID NULL always returns FALSE. C. CUR-PCP-PROV-ID = NULL returns TRUE when CUR-PCP-PROV-ID is NULL, but there are no NULL values in CUR PCP PROV ID D. CUR PCP_ PROV ID NULL returns FALSE when CUR PCP_ PROV ID is NULL, so all values in CUR PCP PROV ID are NULL