When writing recommendation letters you should?
a. limit your remarks to provable facts
b. never collaborate with the former employee in developing the letter
c. never verify anything except the dates of employment and job titles
d. omit all negative information
e. never offer to provide a personal reference?

A. Limit your remarks to provable facts.

Explanation:

The idea of a recommendation letter is to prove to an institution the reasons why an individual is qualified to be accepted there. This implies the institution will count on the individual's skills to develop in their organization as they learn from them via the recommendation letter.

Exaggerating the individual's qualities can be detrimental to their acceptance, as the organization will probably ask for evidence of any unusual skills, or would either pressure them into performing overly hard once they're accepted.