B1
If people or things fill a space, there are a lot of them in it.
Dictionary examples:
Colorful balloons filled the office, making it look like a birthday party. (0.0)
Gigantic teddy bears filled the classroom, surprising the students. (0.0)
Thousands of rubber ducks filled the river during the funny race. (0.0)
The streets were filled with tourists. (14.4)
Dark clouds filled the sky. (52.1)