Scientists observe making the most of our senses when we are young can keep us healthy later on in life.
A. if
B. what
C. that
D. When
网友回答
A. if
B. what
(答案→)C. that
D. When
解析：考查从句关系词的选择。根据句子结构可知observe后面的是宾语从句，从句中不缺少成分，所以选择that，if意为是否 what作主语或者宾语 when作时间状语