Which of the following can be used to transmit CW in the amateur bands?

All of the listed options can indeed be used to transmit Continuous Wave (CW) in the amateur bands, which is an important aspect of amateur radio operation.

A straight key is the most traditional method for sending CW. It consists of a simple mechanism that, when pressed, completes a circuit to send Morse code signals. This method requires the operator to manually control the timing of the keying, which allows for individual expression in the sending speed and style.

An electronic keyer, on the other hand, is a more advanced device that can automate the process of sending Morse code. It typically allows the operator to send code at a consistent speed and offers features such as automatic paddle operation. This can reduce the physical strain on the operator and increase the efficiency and accuracy of transmissions.

Additionally, a computer keyboard can also be used to transmit CW, especially when connected to software that translates keyboard input into Morse code. Many modern amateur radio setups incorporate digital modes, allowing operators to use software to manage their transmissions, which includes CW.

The inclusion of all these options demonstrates the versatility in techniques available to amateur radio operators for CW transmission, accommodating varying levels of skill and preference. Thus, the correct answer reflects the fact that various methods can be employed to effectively transmit