Which of the following is a warning sign for cancer?

All the options listed are indeed warning signs for cancer. Each one pertains to changes that may indicate an underlying health issue, which is why they are part of the "warning signs" to watch out for.

The presence of a new solid lump that is often painless is a common indicator of potential malignancies. Many types of cancer, such as breast cancer or testicular cancer, can present as a painless lump in various parts of the body, signaling the need for further evaluation.

A change in bowel habits can point to gastrointestinal cancers, such as colorectal cancer. This could mean changes in frequency, consistency, or appearance of stools, which could signify abnormal growths or lesions in the digestive system.

Changes in the color of a wart or mole are critical to monitor since they may indicate skin cancers like melanoma. Changes in size, shape, or color of existing moles can be warning signs that should prompt further dermatological assessment.

Since each of these signs can be significant indicators of cancer, it is essential to recognize that they collectively support the understanding of cancer warning signals, hence why the answer encompasses all of the above options.