Abstract: An object is to prevent an operation defect and to reduce an influence of fluctuation in threshold voltage of a field-effect transistor. A field-effect transistor, a switch, and a capacitor are provided. The field-effect transistor includes a first gate and a second gate which overlap with each other with a channel formation region therebetween, and the threshold voltage of the field-effect transistor varies depending on the potential of the second gate. The switch has a function of determining whether electrical connection between one of a source and a drain of the field-effect transistor and the second gate of the field-effect transistor is established. The capacitor has a function of holding a voltage between the second gate of the field-effect transistor and the other of the source and the drain of the field-effect transistor.

Abstract: A compound of the structure ##STR1## wherein R.sup.1 and R.sup.2 are each, independently, hydrogen or ##STR2## with the proviso that R.sup.1 and R.sup.2 are not both hydrogen; R.sup.3 is hydrogen, alkyl, aralkyl, --(CH.sub.2).sub.q CO.sub.2 R.sup.6,--(CH.sub.2).sub.r NR.sup.7 CO.sub.2 R.sup.8, carbamylalkyl, aminoalkyl, hydroxyalkyl, guanylalkyl, mercaptoalkyl, alkylthioalkyl, indolylmethyl, hydroxyphenyklmethyl, imidazoylmethyl or phenyl which is optionally mono-, di-, or tri-substituted with a sustituent selected from alkyl, alkoxy, hydroxy, cyano, halo, nitro, carbalkoxy, trifluoromethyl, amino, or a carboxylic acid;R.sup.4 and R.sup.7 are each, independently, hydrogen, alkyl, or aralkyl;R.sup.5, R.sup.6, and R.sup.