we will be for ------ promises to volunteer to help us solve the puzzling problem.
问题描述：
we will be for ------ promises to volunteer to help us solve the puzzling problem.
为什么用whoever,而不能用those who
具体点,
答
whoever 是指任何人,不限定范围
而those who表示的是那些人,限定了一定的范围,本题应该用whoever