So total ways of selecting and permuting 'dashes' and 'dots' are:
(i) 7 dots ⇒7!7!=1
(ii) 6 dots 1 dashes ⇒7!6!1!=7
(iii) 5 dots 2 dashes ⇒7!5!2!=21
(iv) 4 dots 3 dashes ⇒7!4!3!=35
(v) 3 dots 4 dashes ⇒7!3!4!=35
(vi) 2 dots 5 dashes ⇒7!2!5!=21
Total ways of arranging is 1+7+21+35+35+21=120
Hence, (C)