Which of the following actions may be regarded as Mubah?

Mubah is an Arabic word that refers to actions that are considered to be permissible or allowed in Islam. These are actions that are not explicitly forbidden in the Qur'an or Hadith, and as such, they are not considered to be sinful or wrong. The acquisition of knowledge is considered to be a mubah action because it is encouraged and highly valued in Islam. By gaining knowledge, a person can improve their understanding of their faith and become a better person. On the other hand, actions such as smoking and shaking hands while greeting are not specifically defined as mubah or haram (forbidden) in Islamic teachings, but they may be discouraged or restricted based on the interpretation of different scholars.