Bay lau nay toi cung ban lam , viec gui bai len trang Vat ly ( ViOlet. VN ) co phan han che , du kien sang nam on dinh gia dinh toi se la thanh vien dong gop nhieu bai giai hay trong ch[r]
(1)Thu gui Thay Nguyen van Hung Trung Tam GDTX Huyen Cam Giang