铸造支架中，设置舌杆连接时，杆与余留牙龈缘的正确关系是 （）

A.杆的上端离开余留牙牙龈≤3mm

B.杆的下端离开余留牙牙龈≥3mm

C.杆的上端离开余留牙牙龈必须≥6mm

D.杆的上缘与余留牙牙龈轻微接触

E.杆的上端离开余留牙牙龈≥3mm

Where is Mr.Green?（）the library.

A.He's gone to

B.He's been to

C.He isn't in

D.He's out