1) Roamingcattle posea threat to motorists.
2) Roamingcattles posea threat to motorists.
3) Roamingcattle posesa threat to motorists.
4) Roamingcattles posesa threat to motorists.
5) None of these
Rule ⇒ Certain collective nouns, though singular in form, are always used in the plural sense and take a plural verb. For example, gentry, cattle, poultry, alphabet, offspring etc. Thus, though ‘Cattle’ is a collective noun, it will take plural verb ‘pose’.