Each trace consists of a flat, narrow part of the copper foil that remains after etching. The resistance, determined by width and thickness, of the traces must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than signal traces. In a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in the form of stripline and microstrip with carefully controlled dimensions to assure a consistent impedance. In radio-frequency and fast switching circuits the inductance and capacitance of the printed circuit board conductors become significant circuit elements, usually undesired; but they can be used as a deliberate part of the circuit design, obviating the need for additional discrete components.
What type of trace is often narrower than a ground trace?
signal

Chain department stores grew rapidly after 1920, and provided competition for the downtown upscale department stores, as well as local department stores in small cities. J. C. Penney had four stores in 1908, 312 in 1920, and 1452 in 1930. Sears, Roebuck & Company, a giant mail-order house, opened its first eight retail stores in 1925, and operated 338 by 1930, and 595 by 1940. The chains reached a middle-class audience, that was more interested in value than in upscale fashions. Sears was a pioneer in creating department stores that catered to men as well as women, especially with lines of hardware and building materials. It deemphasized the latest fashions in favor of practicality and durability, and allowed customers to select goods without the aid of a clerk. Its stores were oriented to motorists – set apart from existing business districts amid residential areas occupied by their target audience; had ample, free, off-street parking; and communicated a clear corporate identity. In the 1930s, the company designed fully air-conditioned, "windowless" stores whose layout was driven wholly by merchandising concerns.
How many stores was J. C. Penny operating in 1930?
1452

Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the pigeon, finch, mousebird, button-quail and bustard families are capable of sucking up water without the need to tilt back their heads. Some desert birds depend on water sources and sandgrouse are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers. Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called crop milk that they provide to their chicks.
What is a nutritive fluid that some birds provide to their chicks?
crop milk