Darcy Grafton, CFA, purchases a large block of stock on behalf of specific accounts she managed. The stock realized a significant gain in value before the close of business; so Grafton reviewed her accounts again to determine where the block shares should be allocated. According to the Standards of Practice Handbook, Grafton’s most appropriate action is to allocate the shares to:()

A．all accounts equally.

B．all accounts for which she has discretionary authority.

C．only those accounts for which the block shares were originally intended.

如图所示，O点为轻质杠杆AC的支点．AB=BO=OC，B处挂一重为6牛的小球．若要使杠杆在水平位置平衡，若用最小的力使杠杆在水平位置平衡，则该力的大小为______牛，方向为______．