Can you start a sentence with abbreviation?

It depends on what you mean by "abbreviation." If you mean a shortened form of a word, then yes, you can start a sentence with an abbreviation:

* U.S. history is fascinating.

* Dr. Smith is a renowned surgeon.

However, if you mean a more informal abbreviation or acronym, it's generally considered bad grammar to start a sentence with it:

* LOL, that's a funny story! (Better: That's a funny story, LOL!)

* ASAP, please send me the report. (Better: Please send me the report ASAP.)

Ultimately, whether or not you can start a sentence with an abbreviation depends on the specific abbreviation and the context. It's generally best to err on the side of caution and avoid starting sentences with abbreviations unless it's a well-established and widely accepted practice.