题干
.It was in the 1990s _______ we were working together ____ we made friends with each other.
A：that; whe
B：when; that
C：that; that
D：when; whe
答案(点此获取答案解析）
B
的图象与
轴，
轴分别相交于A，B两点，点C在AB上以每秒1个单位的速度从点B向点A运动，同时点D在线段AO上以同样的速度从点A向点O运动，运动时间用
（单位：秒）表示．