With reference to the Tughlaqs, consider the following statements:

a. Muhammad Bin Tughlaq increased the land revenue of the farmers of the Ganga-Yamuna Doab.

b. Firuz Shah Tughluq started the scheme of takkavi loans to promote agriculture.

c. Muhammad Bin Tughlaq established a new department called Diwan-i-Kohi for agricultural development.

d. Firuz Shah Tughluq was the first Sultan to impose irrigation tax.

Which of the statements given above is/are correct?