Read and write. （根据上下文的意思在横线上填上适当的内容，将对话补充完整）

A: What 1.________ these?  

B: These are my pants.

A: Where are my shorts?          

B: What 2._________ are they?

A: 3._________ 4. _________ black and white.

B: Look, they are on the bed.

有关溃疡性结肠炎的论述哪项是错误的

A．本病在我国发生率较低，病情较轻

B．是发生于直肠和结肠的原因未明的慢性炎症性疾病

C．可有发热、腹痛，腹泻、里急后重等症状

D．常伴有肠外表现

E．病变常累及黏膜下层及肌层