\[\begin {array} {1 1} (a)\;\bigg[\frac{1}{n^{2/3}}-1\bigg] & \quad (b)\;\bigg[1-\frac{1}{n^{1/3}}\bigg] \\ (c)\;\bigg[n^{2/3}-1\bigg] & \quad (d)\;\bigg[n^{4/3}-1\bigg] \end {array}\]