简单用latex3实现了一下，可选参数是留白的比例 13行那个`>`是>，网页bug ```tex \documentclass{ctexart} \usepackage{xeCJKfntef} \usepackage{xparse} \usepackage{xstring} \ExplSyntaxOn \int_new:N \l_wd_int \tl_new:N \l_answer_tl \str_new:N \l_answer_str \NewDocumentCommand{\answer}{O{0} m}{ \tl_set:Nx \l_answer_tl {#2} \int_set:Nn \l_wd_int {\fp_eval:n {floor(#1 * \str_count:N \l_answer_tl)}} \str_set:Nx \l_answer_str {#2} \int_while_do:nn {\l_wd_int > 0}{ \str_put_right:Nn \l_answer_str {烫} \int_decr:N \l_wd_int } \CJKunderline[hidden]{\l_answer_str} } \ExplSyntaxOff \def\test{答案答案答案答案答案答案答案答案答案答案答案答案答案答案} \begin{document} 答案：\CJKunderline{\test} 答案：\CJKunderline[hidden]{\test} 答案：\answer{\test} 答案：\answer[0.5]{\test} 答案：\answer[1]{\test} \end{document} ```