Помогите, пожалуйста)
Choose the right variant.
1.Two (million/millions) euros is difficult to earn.
2. About 4 (million/millions) people live in this city
3.(million/millions) of tourists come to our country is summer
4. Three (hundred/hundreds) students helped the farmers in autumn
5. It has been found that walking ten (thousand/thousands) steps a day will help you drop undesired pounds.
И если не сложно, то объясните, каким правилом вы руководствовались?