Isoelectic focussing is an old but nevertheless useful technique of separating proteins along a gel strip containing an immobilised pH gradient.

In an experiment utilising this technique, a mixture of four proteins (with known pI values of: 9.3, 8.1, 6.5, and 4) was added to the gel strip and an electric field applied. Then, the gel was stained so that proteins could be visualised.

From the image below (where black ovals represent the stained and visualised proteins), which gel strip represents the one corresponding to the above mixture of proteins?