brain-teaser

n difficult problem; puzzle 困难问题; 难题.

bracken, bracket, brackets, brackish, bract, brad, bradawl, brae, brag, braggadocio, braggart, brahmin, braid, braided, braiding, Braille, brain, brain fever, brain-child, brain-drain, brainless, brainpower, brains trust (US brain trust), brainstorm, brainstorming, brainwash, brainwashing, brainwave, brainy, braise, brake, brake fluid, brake light (US stoplight), brake pedal, brake-horsepower, brake-shoe, bramble, bran, bran-tub, branch,