Tokyo stocks sank Monday morning, with the Nikkei index giving up early gains, after the Bank of Japan’s quarterly business sentiment survey showed Japanese companies are cautious about the upcoming three-month period. The 225-issue Nikkei Stock Average fell 604.22 points, or 1.50 percent, from Friday to 39,765.22. The broader Topix index was down 52.15 points, or 1.88 percent, at 2,716.47. The U.S. dollar moved narrowly in the lower 151 yen zone in thin trading, with some overseas markets still closed due to holidays, dealers said. At noon, the dollar fetched 151.32-33 yen compared with 151.3…