Choose the best word or use of words for the blank space that fits the meaning of the sentence as a whole.
For centuries animals have been used as ____ for people in experiments to assess the effects of therapeutic and other agents that might later are used in humans.
আপনি আমাকে যেকোনো প্রশ্ন করতে পারেন, যেমনঃ
Are you sure to start over?