What are the four steps of the calvin cycle?

1. 6 carbon dioxide molecules combine with six 5-carbon molecules forming twelve 3-carbon molecules.
 2. The 12x 3-carbon molecules are converted into high-energy forms.
3. 2 of the 12 3-carbon molecules are removed and the plant uses them to produce sugars, lipids, amino acids, and other compounds.
 4. The 10x 3-carbon molecules change back into six 5-carbon molecules, which combine with 6 more carbon dioxide molecules. The process starts over.

option a is correct i.e.

only sodium ions can pass through the membrane.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.