Spelling changes (Indefinido / Subjuntivo)
Verbs in -car, -gar and -zar change their spelling before an e to keep the sound of the consonant — c → qu, g → gu, z → c — and verbs in -guar add a diaeresis. That e comes in the yo form of the indefinido and in the whole presente de subjuntivo: busqué, busque; llegué, llegue; empecé, empiece.
The card. The back shows the yo form of the Pretérito Indefinido and of the Presente de Subjuntivo. The book opens the verb's conjugation at those two tenses.
The deck. Every verb in your selection in -car, -gar, -zar or -guar whose indefinido is otherwise regular. About one card in five is a regular verb — twenty irregulars bring five — drawn afresh each time you open the drill, so you have to decide whether the verb departs at all.
Grading and the session work as in Future stem (Futuro / Condicional), and each graded card is recorded once for every form on its back.