Definition: to notice something Level: C1
杰克注意到他哥哥脸上焦虑的表情。
Jack ___observed a look of anxiety on his brother's face.
警卫没有注意到谁交付了包裹。
The guards failed to ___observe who delivered the package.
在社会群体之间可以观察到言语风格的差异。
Differences in speech styles can be ___observed between social groups.
