以下代码段中，获取鸢尾花花瓣长度和宽度，正确的表达是______。import tensorflow as tfimport numpy as npimpor pandas as pdTRAIN_URL = "http://download.tensorflow.org/data/iris_trainning.csv"train_path = tf.keras.utils.get_file(TRAIN_URL.split('/')[-1], TRAIN_URL)df_iris_train = pd.read_csv(train_path, header=0)iris_train = np.array(df_iris_train)
选项：

A:x_train = iris_train[:, 2:4];
B:x_train = iris_train[:, 3:4];
C:x_train = iris_train[2:4, :];
D:x_train = iris_train[3:4, :]