Select the correct statement concerning plants that utilize $C_4$ photosynthesis
A. They only open their stomata at night
B. They use bundle sheath cells to separate the Calvin cycle from the atmosphere
C. They use rubisco (ribulose bisphosphate carboxylase oxygenase) to capture carbon dioxide from the atmosphere
D. They use lenticels exclusively for gaseous exchange in order to conserve water
E. All of the above is true

Hint: One of $G_3P$'s three-carbon molecules leaves the cycle to become a member of a molecule of carbohydrates. The remaining $G_3P$ molecules remain in the cycle, which is ready to react with more $CO_2$, to be formed back into RuBP. With the cellular respiration process, photosynthesis forms a balanced cycle of energy.

Complete step by step answer:
Only at night, CAM plants demonstrate temporal separation of photosynthesis and open stomata. Spatial separation of carbon dioxide fixation and RUBISCO activity in mesophyll and bundle sheath cells of $C_4$ plants in $C_4$ plants prevent photorespiration, respectively, by concentrating $CO_2$ in bundle sheath cells to reduce RUBISCO's oxygenase activity and increase the efficiency of RUBISCO .The mesophyll cell PEP carboxylase enzyme fixes carbon dioxide and malate joins the Calvin cycle only in the bundle sheath cells.

Additional information: $C_4$ plants are unusual because they incorporate another type of carbon fixation that, before they undergo the Calvin cycle, forms a four-carbon sugar (hence their name). The Calvin cycle happens in the bundle-sheath cells in the $C_4$ plants (this happens in the mesophyll cells in the $C_3$ plants).
Hence, option B: They use bundle sheath cells to separate the Calvin cycle from the atmosphere is the correct answer.

Note: How do $C_4$ plants help prevent photorespiration by conducting the Calvin cycle only in the bundle sheath cells? Through removing carbon fixation from the steps producing O_2, it helps. By retaining the $CO_2$ until night in the bundle sheath cells, it helps.