TCA9548A I2C Multiplexer - 10k resistors on the address lines
They are just simple pull-down resistors, used to set the default value of the device address.

You can buy multiple of these boards, hook them up to the same bus and give them different addresses by pulling the lines high (note the solder pads on back side of the board).

10K value is a standard pull-up/pull-down resistor value, but anything between 5K and 100K would work just as well.