Why were the Texas colonists “cruelly disappointed"?
The Mexican government had taken away
their land.
The Mexican government did not write a
constitution for them.
The Mexican government had not kept its
promise to protect their rights.

The Texas colonists were cruelly disappointed  because the Mexican government had not kept its promise to protect their rights.

The Texas colonist were the people of Texans which were dominated by the Mexican authority prior to its Independence and integration into the U.S in late 1800s.

Hence, the Texas colonists were cruelly disappointed  because the Mexican government had not kept its promise to protect their rights.

Therefore, the Option C is correct.

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would not cooperate with each other voluntarily.