Simplify the following text for a Grade 3 native English-speaking person.
Original: The second stage will be either a Briz-KM ( Angara 1.1 ) or Block I ( also called URM-2 ) , which is powered by the RD-0124A engine developed by the KB Khimavtomatika . Angara 5 will use either the Briz-M upper stage ( currently used for the Proton-M rocket ) , or KVRB .
Simplified: The second part ( called the second stage ) of Angara 1.1 is called Briz-KM and the second stage of Angara 5 is called Block I.