She has made herself master of flower arranging.

He is a great authority on economics.

He is a master of English literature.

He is a recognized authority on the subject.

The landlord says he wants to raise the rent.

To persuade somebody that your recommendation is reasonable and wise, you have to give reasons and quote known examples and authorities.

It happened that we met the owner of the flat.

They say the landlord used to be well off.

He is an authority on physics.

It became so that I had to hide from the landlord.

Sometimes the old landlady would come by and said "That child doesn't cry", but it was that my babysitting was godly.

The tenant must pay the landlord the rent at the end of each month.

It was unheard of for a literary master, of all people, to get in financial trouble and fall in ruins.