—I'm dead tired. I can't walk any further, Jenny.
—____, Tommy. You can do it.
A:No problem
B:No hurry
C:Come on
D:That's OK
若一对夫妇所生育子女中,性状差异很多,这种变异主要来自( )
手术摘除小白兔的垂体后,其甲状腺功能衰退的原因是( )