Cacti are unusual plants. They grow in extremely hot, dry areas like deserts and they use as little water as possible. Their leaves have become spines and their stems are green like leaves of other plants are. Cacti store water in their thick stems.
A cake is a kind of sweet, baked food. Cakes can be made with all sorts of different ingredients, such as fruit and nuts. The cake in the picture has been decorated with candles, for someone's birthday. There is usually one candle for every year the person has lived.
A calculator is a small device that does math for you. Calculators have built-in functions from simple addition and subtraction right through to complex angle manipulation functions.
A caltrop is common name given to some (unrelated) plants that have seed heads with 4 or more sharp spikes, arranged so that one of them is always pointing upwards. The seed heads are very painful to step on.
Metal devices of the same name and design can be thrown onto roads in front of cars to burst their tires.
Camels are a large animal that is very well adapted for hot, dry weather. They can survive longer without water than any other animal. Camels have a big, fatty hump on their backs that stores food for times when they can't find enough to eat. They are taller than an adult man and are used to ride on or to pull carts.
There are two types of camel, dromedary camels like in the picture that only have one hump, and the bactrian which has two. There are a lot more dromedaries than bactrians in the world.
