Fill in the blanks with the most appropriate option:-

You need to pick either the white one or the blue one. You _________ have both.

can't

The most appropriate option to fill in the blanks is can't.

The sentence is about a restriction on what the speaker can do. The modal verb "can't" is used to express inability or lack of permission. It is the most appropriate modal verb to use in this context, as it describes the fact that the speaker is not allowed to have both the white one and the blue one.

The other options are not as appropriate:

• Shall not is used to express a prohibition or restriction. It is not as appropriate as "can't", as it does not convey the same sense of impossibility or lack of choice.
• Must not is used to express a strong obligation or requirement. It is not as appropriate as "can't", as it does not convey the same sense of inability or lack of permission.
• Shall is used to express a prediction or intention. It is not as appropriate as "can't", as it does not convey the same sense of restriction or prohibition.