Analogy type questions:
$(1)$ $C_4$ plants : Show $CO_2$ saturation at $360 \,\mu l L^{-1}$ :: $C_3$ plants : Show $CO_2$ saturation at concentrations above ............
$(2)$ Green plants : $H_2O$ as hydrogen donor :: Green sulfur bacteria : ............

• A
  $(1) 450 \,\mu l L^{-1}, (2) H_2S$
• B
  $(1) 360 \,\mu l L^{-1}, (2) H_2O$
• C
  $(1) 450 \,\mu l L^{-1}, (2) CO_2$
• D
  $(1) 200 \,\mu l L^{-1}, (2) H_2S$