Part Ⅱ Structure Directions:This part is to test your ability to construct grammatically correct sentences. It consists of 2 sections. Section A Directions:In this section, there are 10 incomplete sentences. You are required to complete each one by deciding on the most appropriate word or words from the 4 choices marked A, B, C and D. Then you should mark the corresponding letter on the Answer Sheet with a single line through the center.
Since nobody is answering the phone, they （）.
A．should have left B．must have left C．need have left D．can have left