It's cold today, so the guitar may be out of tune.

Haven't you touched a guitar or strings in a while? The best maintenance is to play more. . That is, creatures, such as people, lie in bed for a long time, and their muscles will contract.

The weather may be the reason, but the tension of the strings is not very good. If the three strings can't be tuned to the standard tone, then turn down the other strings a little. After playing for a while, you should be able to tune the tone or change the string directly.