On our arrival we found Tom at the desk and a letter.A. seated wroteB. sitting writtenC

问题补充：

On our arrival, we found Tom at the desk and a letter.

A. seated, wrote

B. sitting, written

C. seating, writing

D. seated, writing

答案：

A. seated, wrote

B. sitting, written

C. seating, writing

(答案→)D. seated, writing

解析：考查宾语补足语用法。Seat是及物动词（使…就坐）；sit是不及物动词（就坐）；seated是形容词，在句子中做宾语补足语，说明Tom的情况。第一空也可以使用sitting.Tom和write构成主动关系，所以使用现在分词的形式。句意：我们一到达，就发现Tom在桌子旁边在写信。