What are the names of these organic compounds

a)CH3-CH(Ch2)(Ch3)-Ch2-Ch(Ch3)-Ch3
b) Ch3-C(Cl)(Ch3)-ch2-ch3
c) Ch3-ch2-ch(ch3)-ch3
d)Ch3-ch2-ch(C2h5)-Chch3-Ch(Ch3)2

what i think
a) 2, 4-dimethylhexane
b) 2 –methyl-chlorobutane
c) 2-methylbutane
d) 2-diethyl pentane
I have no idea?

a) correct, 2,4-dimethylhexane
b) incorrect, 2-chloro-2 methylbutane
c) correct, 2-methylbutane
d) incorrect, 4-ethyl-2,3-dimethylhexane

a) Incomprehensible

(b) 2-Chloro-2-methylbutane

c) Correct

d) 2,3-Dimethyl-4-ethylhexane

You must overcome your sloppiness in writing structures. The graders ofr your hour exams will not be forgiving.