It was discovered that the bookkeeper for U Ltd$.$ had recorded a $$200$ deposit from a customer for service work to be performed in the future as follows: Dr$.$ Unearned revenue $$200$; Cr$.$ Cash $$200.$ As a result of this entry

$($a$)$ Cash is understated by $$200$ and Unearned revenue is understated by $$200.$

$($b$)$ Cash is understated by $$400$ and Unearned revenue is overstated by $$400.$

$($c$)$ Cash is understated by $$400$ and Unearned revenue is understated by $$400$

$($d$)$ Cash is understated by $$200$ and Unearned revenue is overstated by $$200.$