def get_edges_by_bond_type(G, bond_type):
    """
    Return edges of a particular bond type.

    Parameters:
    ===========
    - bond_type: (str) one of the elements in the variable BOND_TYPES

    Returns:
    ========
    - resis: (list) a list of tuples, where each tuple is an edge.
    """
    resis = []
    for n1, n2, d in G.edges(data=True):
        if bond_type in d["kind"]:
            resis.append((n1, n2))
    return resis