* The volunteer's altruism was evident in her tireless work at the homeless shelter. (This sentence highlights the action that demonstrates altruism.)
* Motivated by pure altruism, the doctor offered free medical care to the impoverished community. (This sentence emphasizes the motivation behind the altruistic act.)
* True altruism requires selfless acts that benefit others without expecting any personal gain. (This sentence defines altruism in a general sense.)
Remember, "altruism" is a noun. You can also use it in a sentence as an adjective by using the word "altruistic":
* The altruistic donations to the charity helped fund vital programs for the needy.
Choose the sentence that best fits your intended meaning and context.