Which abbreviation should be preferred to indicate "because" when starting a sentence?

The preferred abbreviation to indicate "because" when starting a sentence is "bc." Although "cause," often used in casual contexts and text messaging, can convey the meaning of "because," it is generally not recommended to start a sentence with an informal abbreviation, especially in professional or academic writing.

Using "bc" is widely recognized as a shorthand for "because" and is typically acceptable in many informal contexts. Its use provides a balance between brevity and clarity. Meanwhile, "cuz," "cos," and "cause" tend to lack the same level of formal recognition and can be perceived as overly casual or less professional when included at the beginning of a sentence.

Thus, "bc" is the more suitable choice when aiming for clarity and appropriateness in a written setting.