Who did the teacher-----the letter of thanks for thw whole c

C
句意：老师叫谁向全班同学写了感谢信?
have sb do 叫某人做某事；只是此句中的sb.被疑问词who代替了.原句还原成陈述句则为：
The teacher had (have) who (write ) the letter of thanks for the whole class.