Select all code fragments that correctly implement the pseudocode below.

1. Obtain reading by calling sensor_read()
2. Check if reading is empty (none)

   1. It is empty - wait for 2 seconds and repeat step 1
   2. It is not empty - proceed to step 3

3. Check if reading is between 20 and 25 (inclusive)

   1. If it is, wait for 2 seconds and repeat step 1
   2. If it isn't, call adjust_environment(reading) and pass the reading value to it, then wait 2 seconds and repeat step 1

4. At any time, Ctrl+C to exit the program.