Which of the underline expressions is the hedging of the following sentences.There is experimental work to show that a week or ten days may not be long enough and a fortnight to three weeks is probably the best theoretical period.

A、There is experimental work to show that a week or ten days may not be long enough and a fortnight to three weeks is probably the best theoretical period.;
B、There is experimental work to show that a week or ten days may not be long enough and a fortnight to three weeks is probably the best theoretical period.;
C、There is experimental work to show that a week or ten days may not be long enough and a fortnight to three weeks is probably the best theoretical period.;
D、There is experimental work to show that a week or ten days may not be long enough and a fortnight to three weeks is probably the best theoretical period.