Read this: The pagan Slavic populations were Christianized between the 6th and 10th centuries. Orthodox Christianity is predominant in the East and South Slavs, while Roman Catholicism is predominant in West Slavs and the western South Slavs. The religious borders are largely comparable to the East–West Schism which began in the 11th century. The majority of contemporary Slavic populations who profess a religion are Orthodox, followed by Catholic, while a small minority are Protestant. There are minor Slavic Muslim groups. Religious delineations by nationality can be very sharp; usually in the Slavic ethnic groups the vast majority of religious people share the same religion. Some Slavs are atheist or agnostic: only 19% of Czechs professed belief in god/s in the 2005 Eurobarometer survey.

What religion is predominant in the West and western South Slavs?
What is the answer? (If it cannot be answered, return "unanswerable")
Roman Catholicism