研究地球上生物进化的直接证据是( )
A:比较解剖
B:细胞研究
C:进化树
D:化石
She thought it was worthwhile for her to teach in the small village to make a ______ to the life of the children there.
空闲时聊聊天,吃饭时拍个照片发朋友圈,看到二维码扫一扫。据统计,目前国内微信活跃用户已达5亿人。这种便捷的交流方式源于( )
I ____ to school at 6:30 today.