  Here is the Python code based on the given instructions:
```
import expyfun

# Set up the experiment
experiment_name = "CRM_Experiment"
window_size = 10
participant = "John"
session = "01"
version = "1.0"

# Prepare the corpus
crm_prepare_corpus(window_size, participant, session, version)

# Load the talkers
talker1 = expyfun.CRMPreload("talker1", window_size)
talker2 = expyfun.CRMPreload("talker2", window_size)

# Print the valid callsigns
print(talker1.callsign)
print(talker2.callsign)

# Read a sentence from the hard drive
sentence1 = crm_sentence(talker1.callsign, window_size)
sentence2 = crm_sentence(talker2.callsign, window_size)

# Pad and align the sentences
sentence1_padded = sentence1.pad(window_size)
sentence2_padded = sentence2.pad(window_size)

# Preload all the talkers
talker1.preload()
talker2.preload()

# Get a second sentence from memory
sentence3 = talker1.get_sentence(window_size)
sentence4 = talker2.get_sentence(window_size)

# Pad and align the second sentence
sentence3_padded = sentence3.pad(window_size)
sentence4_padded = sentence4.pad(window_size)

# Display a text prompt on the screen
screen_prompt("Press any key to start the experiment")

# Load the padded sentences into the buffer
load_buffer(sentence1_padded, sentence2_padded, sentence3_padded, sentence4_padded)

# Start the stimulus
start_stimulus()

# Wait for a specific duration
wait_for_click_on(experiment_name)

# Display a prompt based on the response
response = crm_response_menu(window_size)
if response == "1":
    screen_text("You pressed the first button")
elif response == "2":
    screen_text("You pressed the second button")
else:
    screen_text("You pressed neither button")

# Plot a screenshot of the experiment
plot_screen(experiment_name)
```
Note that this code assumes that the `CRMPreload` class is defined in the `expyfun` library, and that the `crm_prepare_corpus`, `crm_sentence`, `crm_response_menu`, and `start_stimulus` functions are also defined in the `expyfun` library.