wèi / le / còu / zú / rén / shù / lǎo / shī / ràng / yí / ge / páng / guān / de / xué / shēng / jìn / chǎng / chōng / shù

为了凑足人数，老师让一个旁观的学生进场充数。

To make up the required number, the teacher let a student who had been watching join in.