计算决定系数R²

def solve():
    from sklearn.datasets import load_iris
    import numpy as np
    iris = load_iris()
    x = iris.data[:, ____]
    y = iris.data[:, ____]
    x_mean, y_mean = np.mean(____), np.mean(____)
    slope = np.sum((____) * (____)) / np.sum((____) ** ____)
    intercept = y_mean - slope * x_mean
    y_pred = slope * x + intercept
    ss_res = np.sum((____) ** ____)
    ss_tot = np.sum((____) ** ____)
    r2 = ____ - ss_res / ss_tot
    print(____)