In which of the following cases, the bid bond will not be forfeited （ ）
A: If a Bidder withdraws its bid during the period of bid validity specifed by the Bidder onthe Letter of Bid Form.
B: If the successful Bidder fails to sign the Contract as required .
C: If the successful Bidder fails to furnish a performance security as required.
D: Where a bidder modifies his tender documents.