In each of the questions given below, four words are given in bold. These four words may or may not be in their correct position. The sentence is then followed by options with the correct combination of words that should replace each other in order to make the sentence grammatically and contextually correct. Find the correct combination of words that replace each other. If the sentence is correct as it is, select ‘E’ as your option.  The engineers spent several months ensure (

• A and testing a prototype (
• B of the new electric car to building (
• C it met all safety and performance standards before moving to full production (
• D .