After Certifying a Union,the NLRB Sets Certain Limits for Future

After certifying a union,the NLRB sets certain limits for future elections.Which of the following is one such limit?

A) It will not permit additional elections for five years.
B) After the union and employer have finished negotiating a contract, an election cannot be held for the time of the contract period or for two years, whichever comes first.
C) The parties to the contract may agree not to hold an election for longer than three years.
D) After negotiating a contract, union elections cannot be conducted online.
E) An outside party can be barred from holding elections for more than three years.