同位语从句中什么时候用that 什么时候用whether?

同位语从句中什么时候用that 什么时候用whether?
看两个同位语从句：
1.The mother was filled with anxiety _____ her daughter might be disabled by the accident.
A.whether B.that C.what D.which 这题选A
2.A growing anxiety is disturbing the public _____ the economy will continuously decline.
A.which B.that C.why D.whether 这题选B
问：同样都是anxiety的同位语,为什么 第一个选whether,而第二个选that