问题补充：
When I got back home I saw a message pinned to the door “Sorry to miss you; will call later.”
A. read
B. reads
C. to read
D. reading
答案：
A. read
B. reads
C. to read
(答案→)D. reading
解析：句中 read 意为“有某字样”，a message pinned to the door 意为“钉在门上的一张纸条”，a message 与 read 是主动关系，因此用现在分词。
