In the following, when a transaction TT performs an operation x$=$x$+$ax$=$x$+$a$,$ then TT reads xx into some register, adds a to the register content then stores register content into xx$.$

A transaction schedule is serializable if its effect is equivalent to that of some serial schedule. Consider a bookkeeping operation consisting of two transactions $$T$1$T$1$ and T$2$T$2$ that are required to keep the sum A$+$B$+$CA$+$B$+$C unchanged. Which of the following pairs of transactions will always result in a serializable schedule? I. T$1$ : Lock A; A $=$ A $-10$; Unlock A; B $=$ B $+10$; T$2$: Lock B; B $=$ B $-20$; Unlock B; C$=$C$+20$; II$.$ T$$ : A$=$A$-10$; Lock B; B$=$B$+10$; Unlock B; T$2$: Lock B; B$=$B$-20$; Unlock B; C$=$C $+20$; III. T$1$:Lock A; A $=$ A $-10$; Unlock A; B $=$ B $+10$; T$2$: Lock A; B $=$ B $-20$; Unlock A; C$=$C$+20$; OPTIONS: I only

II only

III only

I and II