Can someone check these for me...

Express each of these sets using a regular expression:

a)The set containing all strings with 0, 1, or 2 bits.

$\displaystyle

(\lambda\cup0\cup1\cup00\cup01\cup10\cup11)

$

b)The set of strings of two 0's, followed by zero or more 1's, and ending with a 0

$\displaystyle

001^*0

$

c)The set of strings with every 1 followed by two 0's.

$\displaystyle

(100)^*

$

d)The set of strings ending in 00 and not containing 11. *NOT SURE

$\displaystyle

(00\cup100)^*

$

e)The set of strings containing an even number of 1's. *NOT SURE

$\displaystyle

0^*10^*(10^*)^*

$