Owning pet birds is not just feeding them when necessary. You have to be very responsible if you have decided to keep birds as pets. If you really want to acquire a companion, think in advance whether you are able to handle it. Depending on what pet bird you are going to have and how big it is, the cost is different. For example, the cost of a comfortable cage, the cost for nutritional food and the money for some additional things should be taken into consideration. There are also some unexpected cost. For example, when your pet bird gets sick, you have to send for a vet  . You may think that you do not have free time to have a dog so you'd better have a pet bird because it doesn't require a lot of attention. You are wrong! Some people even do not have time for a short sleep. They will not have enough time for pets, either. For good bird health it is very important to handle them and play with them as much as you can. Also there are a lot of people who think that birds do not require a lot of space and they are wrong again. They also need to fly so if you do not have space for it, you'd better reconsider the things.  But do not forget the great advantage of having a pet bird. In the animal kingdom, birds rank near the top when it comes to smarts. You can have a friend for life if you take good care of it. It's a real character and can bring joy and colour in your home. If you want to have a pet bird, you needn't consider_.
the knowledge about a pet bird the cost of having a pet bird the time taken to care for a pet bird the space a pet bird needs to fly
Question: Owning pet birds is not just feeding them when necessary. You have to be very responsible if you have decided to keep birds as pets. If you really want to acquire a companion, think in advance whether you are able to handle it. Depending on what pet bird you are going to have and how big it is, the cost is different. For example, the cost of a comfortable cage, the cost for nutritional food and the money for some additional things should be taken into consideration. There are also some unexpected cost. For example, when your pet bird gets sick, you have to send for a vet  . You may think that you do not have free time to have a dog so you'd better have a pet bird because it doesn't require a lot of attention. You are wrong! Some people even do not have time for a short sleep. They will not have enough time for pets, either. For good bird health it is very important to handle them and play with them as much as you can. Also there are a lot of people who think that birds do not require a lot of space and they are wrong again. They also need to fly so if you do not have space for it, you'd better reconsider the things.  But do not forget the great advantage of having a pet bird. In the animal kingdom, birds rank near the top when it comes to smarts. You can have a friend for life if you take good care of it. It's a real character and can bring joy and colour in your home. If you want to have a pet bird, you needn't consider_.
A. the knowledge about a pet bird
B. the cost of having a pet bird
C. the time taken to care for a pet bird
D. the space a pet bird needs to fly
Answer: