1.They plan to collect used paper and send them for recycling (Use'be going to')
       They are going to collect used paper and send them for recycling
2.His hair is short and black
     He has short black hair
3.Mary is too young to get married(using 'enough')
    Marry is not old enough to get married
4.We intend to meet her at the airport tonight (Use'be going to')
       We are going to  meet her at the airport tonight