Translate the following Kiswahili sentences into the perfect tense and change the underlined word to its antonym.

Here are the solutions to the Kiswahili grammar questions:

2) Andika kwa ukubwa hali timilifu (alama 3)
Mtego ulimnawa ndovu huyo.

To change this sentence to the perfect tense, we replace the past tense marker '-li-' with the perfect tense marker '-me-'.

• Original verb: ulimnawa (u-li-m-nawa)
• Perfect tense verb: umemnawa (u-me-m-nawa)

The sentence in the perfect tense is:
$\boxed{\text{Mtego umemnawa ndovu huyo.}}$

3) Andika sentensi ifuatayo upya ukibadilisha neno lililopigiwa mstari.
Msichana amecheza vibaya.

The underlined word is 'vibaya' (badly). To change it, we can use its antonym 'vizuri' (well).

The rewritten sentence is:
$\boxed{\text{Msichana amecheza vizuri.}}$