---Answer the doorbell please. It must be your uncle. ---It Heidi. She’s coming over this

问题补充：

---Answer the doorbell, please. It must be your uncle.

---It Heidi. She’s coming over this morning to help me with my math.

A. is

B. can’t be

C. could be

D. will be

答案：

A. is

B. can’t be

(答案→)C. could be

D. will be

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