Answer:

a. Simple present tense.

b. Present continuous tense.

EXPLANATION:

a. Neha ALWAYS completes her projects on TIME.

In this sentence,

Subject = Neha

Verb = completes

We know the STRUCTURE of simple present tense.

i.e., Sub + v1/v5 + object

Here, The sentence is formed by USING the structure of simple present tense.

b. My neighbours are celebrating Christmas with friends this year.

Sub = My neighbors

Verb = are celebrating

We know the structure of present continuous tense.

i.e., Sub + is/am/are + v4 + object

Here, The sentence is formed by using the structure of present continuous tense.

More structure of tense to know:

Simple present tense: Sub + v1/v5 + obj

Present continuous tense: Sub + is/am/are + v4 + obj

Present perfect tense: Sub + have/has + v3 + obj

Present continuous tense: Sub + have/has + been + v4 + since/for + time

Simple past tense: Sub + v2 + obj

Past continuous tense: Sub + was/were + v4 + obj

Past perfect tense: Sub + had + v3 + obj

Past perfect continuous tense: Sub + had been + v4 + since/for + time

Simple future tense: Sub + will/shall + v1 + obj

Future continuous tense: Sub + will/shall + be + v4 + obj

Future perfect tense: Sub + will/shall + have + v3 + obj

Future perfect continuous tense: Sub + will/shall + have been + v4 + since/for + time

Abbreviations used:

v1 = Base form of verb

v2 = Simple past form of verb

v3 = Past participle form of verb

v4 = Present participle form of verb

v5 = Simple present form of verb