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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mark_sentence_boundaries(sequences, drop=0.0):
 # pragma: no cover """Pad sentence sequences with EOL markers."""

    for sequence in sequences:
        sequence.insert(0, "-EOL-")
        sequence.insert(0, "-EOL-")
        sequence.append("-EOL-")
        sequence.append("-EOL-")
    return sequences, None