题干

如图所示,固定斜面C的倾角为θ,物体A放在斜面C上,物体B叠放在物体A上,A、B的质量均为m,且上、下表面均与斜面平行,A、B一起沿斜面匀速下滑,则(   )

A:A与B之间没有静摩擦力

B:A受到B的静摩擦力方向沿斜面向上

C:A与B之间的动摩擦因数μ=tanθ

D:A受到斜面的滑动摩擦力大小为2mgsinθ

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D

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    Most of us have lost our wallet at some stage in our lives. But few would imagine having it returned after 66 years. Edward Parker dropped his wallet in 1950 into an inaccessible spot behind a bookshelf, while working as an electrician, repairing World War Two bomb damage in the palace. The wallet stayed there until this year when a builder, doing some restoration work, finally found it.

    The wallet is a time capsule. Its leather and webbing has long ago started to disintegrate. But it contains numerous pictures of family, invoices, receipts, old union cards, results of a chest X-ray (sent to him in 1948, the same year as the NHS was founded), a national service card dated 9 December 1944 and a medical insurance card. His business cards—E Parker, Electrical Contractor—seem almost original. Reflecting the typical methods of contact of the time, they have an address but no telephone number.

    A month ago I was speaking to a press officer Lambeth Palace and he mentioned that the wallet had just been handed in. We thought it might be nice to try and work out whose it was and give it back to the family. Edward Parker is a pretty common name, but his medical card contained two places of residence—Poets Road and Springdale Road in north London. From this, Islington Council were able to find details of a marriage between Edward Parker and Constance Butler in 1947.

    That information was enough to work out that he was still alive and in a care home in Essex, so I went to visit him. Now 89, Edward has dementia (痴呆), but he was clearly happy to get the wallet and in particular, the photographs back. He pointed out pictures of his mother and father, his brother, his cousins and his wife Constance, who was with him when I visited. He hadn't seen a picture of his father since he lost the wallet, Constance, 90, said.