The correct answer is - oranges take a long time to grow.
The orange tree is a tree needs several years in order for it to be able to develop a fruit, usually three to four years, though it will produce only few fruits in that period, and will only produce more after the tenth year when the tree is fully matured.
The fruit itself also takes a while to mature, pretty much a whole year. So when the friends of Molly say that she is not living sustainable lifestyle it is because she eats oranges all the time, though they are only harvested in one particular part of the year, and it is a long process, referring to that the she uses more than a tree can produce.
