Question: Can only vegetables be added to salad?
About the article "Salad", section "Vegetable salad".

Candidate passages:
Vegetables other than greens may be used in a salad.
Common raw vegetables used in a salad include cucumbers, peppers, tomatoes, onions, spring onions, red onions, carrots, celery, and radishes.
Other ingredients, such as mushrooms, avocado, olives, hard boiled egg, artichoke hearts, heart of palm, roasted red bell peppers, green beans, croutons, cheeses, meat (e.g.
bacon, chicken), or seafood (e.g.
tuna, shrimp), are sometimes added to salads.
Chicken salad is any salad that comprises chicken as a main ingredient.
Other common ingredients may include mayonnaise, hard-boiled egg, celery, onion, pepper, pickles and a variety of mustards.
In the United States, "chicken salad" refers to either any salad with chicken, or a specific mixed salad consisting primarily of chopped chicken meat and a binder, such as mayonnaise or salad dressing.
Like tuna salad and egg salad, it may be served on top of lettuce, tomato, avocado, or some combination of these.
It may also be used for sandwiches.
Typically it is made with leftover or canned chicken.
It may also refer to a garden salad with fried, grilled, or roasted chicken (usually cut up) on top.
In Europe and Asia the salad may be complemented by any number of dressings, or indeed no dressing at all, and the salad constituents can vary from traditional leaves and vegetables, to pastas, couscous, noodles or rice. 
Although potato salad can be served any time in the USA, it is commonly associated with summer picnics.
There are many variations, owing perhaps more to personal preferences than regional or cultural influences.
The basis is always boiled potatoes, usually coarsely cubed and a mayonnaise or mayonnaise-like sauce.
Both white potatoes and red potatoes are popular, and the potatoes may be peeled or left with skin on.
To the basic salad common enhancements include yellow mustard, pickle relish, onions (usually raw), chopped bell peppers and thinly-sliced celery and/or celery seed.
Meat, beans, and other vegetables are usually not included.
The salad is often topped with black pepper or paprika.
The addition of mustard results in a yellowish coloration (see illustration captioned "American-style potato salad) as well as imparting an additional tang to the flavor, depending on the amount added.
When chopped or sliced hard-boiled eggs are included, the salad is often labeled "Southern Style". 
Products include potatoes, soft fruit (strawberries and raspberries).
and prepared vegetables (casserole vegetables and scotch broth).
In March 2013, the company announced the launch of a Coleslaw and Potato Salad.
Further products will be added to the line up, including Salmon  
Types of salads.
Green salad.
The "green salad" or "garden salad" is most often composed of leafy vegetables such as lettuce varieties, spinach, or rocket (arugula).
Due to their low caloric density, green salads are considered a common diet food.
The salad leaves may be cut or torn into bite-sized fragments and tossed together (called a "tossed salad"), or may be placed in a predetermined arrangement (a "composed salad").