If you describe someone as guarded, you mean that they are careful not to show their feelings or give away information. 谨慎的
adjective [原级] （人或言语）谨慎的，有保留的；被监视着的；警戒着的；被看守着的
The boy gave him a guarded look. 这个男孩谨慎地看了他一眼。
verb [vt. 及物动词] 保卫，看守（guard的过去式和过去分词）
Marines with rifles guarded them. 持步枪的海军陆战队士兵看守他们。
