Element X in the circuit below has a resistance  $R_x$  which depends on the voltange  $V_x$  on it: for  $V_x\le 1V,R_x=1\Omega andfor{V}_x>1V,R_x=2\Omega$ . Three such elements are connected with an ideal ammeter as shown below; the voltage on the leads (across a and b) of the circuit varies in time as shown in the graph.

Which of the following combinations of (current, time) is/are possible?
(Reading of ammeter)