Which is correct way to define featuresX = df[['clo1', 'col2', . . .]]X = df[clo1, col2, . . .]X = df['clo1', 'col2', . . .]X = df[[clo1, col2, . . .]]

The correct way to define features in a pandas DataFrame is:

X = df[['col1', 'col2', ...]]

This syntax is used to select multiple columns from a DataFrame in pandas. The double square brackets indicate a list of column names.

The other options are incorrect because:

• X = df[clo1, col2, ...] and X = df[[clo1, col2, ...]]: These are incorrect because the column names are not enclosed in quotes. Python will interpret these as variable names, not column names.
• X = df['col1', 'col2', ...]: This is incorrect because it's trying to access multiple columns with single square brackets, which will result in a KeyError.

So, the correct syntax is to use double square brackets with the column names as strings.