There are two boxes containing only orange and white pens. Box $\mathbf{A}$ has 12 white pens and 4 orange pens. Box $\mathbf{B}$ has 7 white pens and 13 orange pens. A pen is randomly chosen from each box. List these events from least likely to most likely. Event 1: choosing a white or orange pen from Box A. Event 2: choosing a white pen from Box A. Event 3: choosing an orange pen from Box $B$. Event 4: choosing a white pen from Box $B$.

Step 1 ：Calculate the probability of each event:

Step 2 ：Event 1: choosing a white or orange pen from Box A. Probability: \(\frac{16}{16} = 1\)

Step 3 ：Event 2: choosing a white pen from Box A. Probability: \(\frac{12}{16} = 0.75\)

Step 4 ：Event 3: choosing an orange pen from Box B. Probability: \(\frac{13}{20} = 0.65\)

Step 5 ：Event 4: choosing a white pen from Box B. Probability: \(\frac{7}{20} = 0.35\)

Step 6 ：Sort the events from least likely to most likely:

Step 7 ：\(\boxed{\text{Event 4, Event 3, Event 2, Event 1}}\)